High frequency matching system

ABSTRACT

An impedance adjustment apparatus of the invention performs impedance matching using characteristic parameters, even where a high frequency power source of variable frequencies is used. The apparatus is applicable to a power supply system using a high frequency power source of variable frequencies. Characteristic parameters obtained by targeting a portion of combinations of position information (C) of a variable capacitor and output frequency information (F) of the power source are stored in a memory. A T-parameter acquisition unit acquires characteristic parameters corresponding to (C now , F now ) at the current time. An output reflection coefficient calculation unit calculates a reflection coefficient of an output end. A target information specifying unit, based on the above information and a target input reflection coefficient, specifies target combination information in which a reflection coefficient of an output end approaches the target input reflection coefficient. Impedance matching is performed based on this information.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an impedance adjustment apparatus thatis provided between a high frequency power source and a load, and thatadjusts impedance seen from the high frequency power source to the loadside.

2. Description of Related Art

FIG. 8 is a diagram showing an exemplary configuration of a highfrequency power supply system. This high frequency power supply systemis a system for performing a processing process such as plasma etchingor plasma CVD on a workpiece such as a semiconductor wafer or a liquidcrystal substrate, for example. The high frequency power supply systemis constituted by a high frequency power source 1, a transmission line2, an impedance adjustment apparatus 3, a load connecting portion 4, anda load 5 (plasma processing apparatus 5). The impedance adjustmentapparatus may also be called an impedance matching apparatus. The highfrequency power source 1 supplies high frequency power to the load 5 viathe transmission line 2, the impedance adjustment apparatus 3, and theload connecting portion 4. In the load 5 (plasma processing apparatus5), a plasma discharge gas is changed into a plasma state within achamber (not shown) in which the workpiece is disposed, and theworkpiece is processed using the gas that is in the plasma state. Thegas in the plasma state is generated by introducing the plasma dischargegas into the chamber and supplying high frequency power from the highfrequency power source 1 to an electrode (not shown) provided within thechamber to cause the plasma discharge gas to discharge.

With a plasma processing apparatus 5 that is used for applications suchas plasma etching and plasma CVD, the state of the plasma constantlychanges with the progress of the manufacturing process. The changingstate of the plasma results in the impedance (load impedance) of theplasma processing apparatus 5 constantly changing. In order toefficiently supply power from the high frequency power source 1 to sucha plasma processing apparatus 5, an impedance ZL seen from an output endof the high frequency power source 1 to the plasma processing apparatus5 side (hereinafter, load-side impedance ZL) needs to be adjustedfollowing a change in load impedance. For this reason, with the highfrequency power supply system shown in FIG. 8, the impedance adjustmentapparatus 3 is interposed between the high frequency power source 1 andthe load 5 (plasma processing apparatus 5).

The impedance adjustment apparatus 3 is provided with elements havingvariable electrical characteristics such as variable capacitors orvariable inductors. Variable capacitors are capacitors whose capacitancecan be changed. The impedance adjustment apparatus 3 adjusts theload-side impedance ZL by adjusting electrical characteristics such ascapacitance or inductance of the elements having variable electricalcharacteristics. The impedance adjustment apparatus 3 matches the outputimpedance of the high frequency power source 1 and the impedance of theload 5, by setting the electrical characteristics of the elements havingvariable electrical characteristics to suitable values. Matching theimpedances enables the power supplied to the load 5 to be maximized byminimizing reflected wave power directed from the load 5 to the highfrequency power source 1 as much as possible.

Because variable capacitors and variable inductors are elements whoseelectrical characteristics can be adjusted, in the presentspecification, variable capacitors and variable inductors arecollectively referred to as “elements having variable electricalcharacteristics”. Also, information on capacitance, inductance and thelike is referred to as “electrical characteristic information”.

FIG. 9 is a block diagram showing an exemplary configuration of a highfrequency power supply system including a conventional impedanceadjustment apparatus 3P.

A high frequency power source 1 p is connected to an input end 301 ofthe impedance adjustment apparatus 3P by a transmission line 2, and aload 5 (plasma processing apparatus) is connected to an output end 302by a load connecting portion 4. The high frequency power source 1 p is apower source that outputs a high frequency wave having a constant outputfrequency. The output frequency is a fundamental frequency (frequency ofa fundamental wave) of the high frequency wave that is output from thehigh frequency power source 1 p.

As shown in FIG. 9, the impedance adjustment apparatus 3P is providedwith an adjustment circuit 20 p constituted by a first variablecapacitor 21, a second variable capacitor 24, and an inductor 23. Thefirst variable capacitor 21 and the second variable capacitor 24 are onetype of element having variable electrical characteristics. An outputend of the adjustment circuit 20 p is connected to the output end 302 ofthe impedance adjustment apparatus 3P, and a directional coupler 10 isprovided between an input end of the adjustment circuit 20 p and theinput end 301 of the impedance adjustment apparatus 3P.

The high frequency power output from the high frequency power source 1 pis supplied to the load 5 via the directional coupler 10 and theadjustment circuit 20 p provided in the impedance adjustment apparatus3P. Note that high frequency power that is output from the highfrequency power source 1 p and travels to the load 5 is called travelingwave power PF, and high frequency power that is reflected by the load 5and returns to the high frequency power source 1 p is called reflectedwave power PR.

The impedance adjustment apparatus 3P is able to adjust (change) theload-side impedance ZL, by adjusting (changing) the capacitances of thefirst variable capacitor 21 and the second variable capacitor 24provided in the adjustment circuit 20 p. The impedance adjustmentapparatus 3P matches the output impedance of the high frequency powersource 1 p and the impedance of the load 5, by changing the respectivecapacitances of the first variable capacitor 21 and the second variablecapacitor 24 to suitable values. Note that the configuration of theadjustment circuit 20 p differs depending on factors such as the outputfrequency of the high frequency power source 1 p and conditions of theload 5. Variable inductors may be also used as elements having variableelectrical characteristics.

The variable capacitors use for the first variable capacitor 21 andsecond variable capacitor 24 have a movable portion (not shown) foradjusting capacitance. The capacitance of the variable capacitors isadjusted by displacing the position of the movable portion using a motoror the like.

The variable capacitors are provided with a pair of electrodes, at leastone of which is a movable electrode, with the movable electrode beingthe movable portion for adjusting capacitance. Because the size of theopposing area of the movable electrode and the other electrode changeswhen the position of the movable electrode is displaced, resulting in achange in capacitance, the capacitance of the variable capacitor isadjusted (changed) by adjusting (changing) the position of the movableelectrode.

The capacitance of the variable capacitor is configured so as to beadjustable over a plurality steps. The capacitance relative to theposition of the movable portion of the variable capacitor is knownthrough the specifications of the variable capacitor or through testing.Because the capacitances of the variable capacitors are known if theposition of the movable portion is known, position information of themovable portion is used as information representing the capacitances(capacitance information) in adjusting the capacitances of the variablecapacitors. Accordingly, the position information of the movable portionof the variable capacitors is treated as information representingelectrical characteristics of the variable capacitors (electricalcharacteristic information).

The position information of the movable portion of the variablecapacitors may be any information obtained by directly or indirectlydetecting the position of the movable portion. Because it is difficultgiven the structure of the movable portion to directly detect theposition of the movable portion, the position of the movable portion isindirectly detected by, for example, detecting the rotation position(amount of rotation) of the motor that displaces the position of themovable portion. The rotation position of the motor can be detectedusing a pulse signal or voltage that controls the drive of the motor, orthe like.

In the case of FIG. 9, the position of the movable portion of the firstvariable capacitor 21 is adjusted by an adjustment unit 30, and theposition information of the movable portion of the first variablecapacitor 21 is detected (acquired) by a position detection unit 40.Also, the position of the movable portion of the second variablecapacitor 24 is adjusted by an adjustment unit 50, and the positioninformation of the movable portion of the second variable capacitor 24is detected (acquired) by a detection unit 60.

The adjustment unit 30 is a drive means for displacing the position ofthe movable portion of the first variable capacitor 21. The adjustmentunit 30 is constituted by a stepping motor, a motor drive circuit andthe like (all not shown), for example. The motor drive circuit providedin the adjustment unit 30 rotates the stepping motor based on a commandsignal that is input from a control unit 100 p. The position of themovable portion of the first variable capacitor 21 is displaced by therotation of the stepping motor. Accordingly, the control unit 100 padjusts the capacitance of the first variable capacitor 21 bycontrolling the amount of rotation of the stepping motor provided in theadjustment unit 30. Similarly, the adjustment unit 50 is a drive meansfor displacing the position of the movable portion of the secondvariable capacitor 24. The adjustment unit 50 is constituted by astepping motor, a motor drive circuit, and the like (all not shown), forexample. The motor drive circuit provided in the adjustment unit 50rotates the stepping motor based on a command signal that is input fromthe control unit 100 p, and displaces the position of the movableportion of the second variable capacitor 24. Accordingly, the controlunit 100 p adjusts the capacitance of the second variable capacitor 24by controlling the amount of rotation of the stepping motor provided inthe adjustment unit 50.

The position detection unit 40 detects the rotation position (amount ofrotation) of the stepping motor provided in the adjustment unit 30.Similarly, the position detection unit 60 detects the rotation position(amount of rotation) of the stepping motor provided in the adjustmentunit 50.

Note that variable inductors differ in structure from the variablecapacitors, but also have a movable portion, similarly to the variablecapacitors. The variable inductors are also similarly configured to beable to adjust (change) the inductance of the variable inductors bydisplacing the position of the movable portion using a motor or thelike. Because the method used by the variable inductors to vary theinductance is basically the same as the variable capacitors, descriptionthereof will be omitted. Because the inductances are also similarlyknown if the position of the movable portion of the variable inductorsis known, in the case where the variable inductors are used as theelements having variable electrical characteristics, positioninformation of the movable portion of the variable inductors is treatedas information representing the inductances of the variable inductors(inductance information).

The first variable capacitor 21 and second variable capacitor 24 areconfigured to be able to adjust respective capacitances over a pluralityof steps. For example, in the case where the position of the movableportion of the first variable capacitor 21 and the second variablecapacitor 24 can each be displaced over 101 steps, the impedance of theadjustment circuit 20 p can be changed in (101×101=) 10,201 (approx. tenthousand) combinations. That is, the impedance matching apparatus 3P isable to adjust (change) the load-side impedance ZL using approximately10,000 impedance adjustment positions.

In the case where the position of the movable portion of the variablecapacitors is displaced over a plurality of steps, allocating a numberto each displacement position of the movable portion enables thesenumbers to be used as position information of the movable portion of thevariable capacitors. For example, in the case where the position of themovable portion of the variable capacitors is displaced over 101 steps,assuming that the position at which the capacitance is minimized is “0”and the position at which the capacitance is maximized is “100”, theposition information of the movable portion of the variable capacitor isrepresented by the numbers 0 to 100. Accordingly, assuming that theposition information of the movable portion of the first variablecapacitor 21 and the position information of the movable portion of thesecond variable capacitor 24 are each represented by the numbers 0 to100, the impedance adjustment position of the impedance adjustmentapparatus 3P is represented by position information that combines theposition information of the movable portion of the first variablecapacitor 21 and the position information of the movable portion of thesecond variable capacitor 24, such as (0,0), (0,1), . . . , (100,100).

For example, Patent Document 1 (JP 2006-166412A) proposes an impedanceadjustment apparatus 3P that performs impedance matching by controllingelements having variable electrical characteristics such as variablecapacitors or variable inductors.

With the impedance adjustment apparatus 3P disclosed in Patent Document1, characteristic parameters of the impedance adjustment apparatus 3Pthat have been measured in advance are stored in a memory 70 p. Thecharacteristic parameters are parameters indicating transmissioncharacteristics in the case where the entire impedance adjustmentapparatus 3P is regarded as a transmission apparatus, and include, forexample, S-parameters (scattering parameters) and T-parameters(transmission parameters) converted from the S-parameters. Thecharacteristic parameters are measured with respect to all impedanceadjustment positions of the impedance adjustment apparatus 3P (positioninformation combining the position information of the movable portion ofthe first variable capacitor 21 and the position information of themovable portion of the second variable capacitor 24), after adjustingthe impedance adjustment apparatus 3P to the respective impedanceadjustment positions. Accordingly, the measured values of a plurality ofcharacteristic parameters are stored in the memory 70 p in associationwith the impedance adjustment positions. The control unit 100 p thenperforms impedance matching, based on a detection signal of a travelingwave voltage and a detection signal of a reflected wave voltage that areoutput from the directional coupler 10, position information of themovable portion of the first variable capacitor 21 that is detected bythe position detection unit 40, position information of the movableportion of the second variable capacitor 24 that is detected by theposition detection unit 60, and information on the characteristicparameters stored in the memory 70 p.

Because the characteristic parameters are parameters indicatingtransmission characteristics within the impedance adjustment apparatus 3p including stray capacitance and inductance components, accurateimpedance matching can be performed if impedance matching is performedusing the measured characteristic parameters.

TABLE 1 VC1 0 1 2 . . . . . . 98 99 100 VC2 0 T (0, 0) T (1, 0) T (2, 0). . . . . . T (98, 0) T (99, 0) T (100, 0) 1 T (0, 1) T (1, 1) T (2, 1). . . . . . T (98, 1) T (99, 1) T (100, 1) 2 T (0, 2) T (1, 2) T (2, 2). . . . . . T (98, 2) T (99, 2) T (100, 2) . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . 98  T (0, 98)  T (1, 98)  T (2, 98) . . . . . .  T (98, 98)  T(99, 98)  T (100, 98) 99  T (0, 99)  T (1, 99)  T (2, 99) . . . . . .  T(98, 99)  T (99, 99)  T (100, 99) 100  T (0, 100)  T (1, 100)  T (2,100) . . . . . .  T (98, 100)  T (99, 100) T (100, 100)

Table 1 is an example of characteristic parameters stored in the memory70 p. Table 1 shows an example of the case where the characteristicparameters stored in the memory 70 p are T-parameters. In Table 1, theposition information of the movable portion of the first variablecapacitor 21 is represented with a variable VC1, and the positioninformation of the movable portion of the second variable capacitor 24is represented with a variable VC2. Also, the variable range of themovable portion of the first variable capacitor 21 and the variablerange of the movable portion of the second variable capacitor 24 arerespectively ranges of 0 to 100 (101 steps).

In Table 1, T(0,0) indicates the T-parameter measured after adjustingthe impedance adjustment apparatus 3P to an impedance adjustmentposition (0,0) (adjustment position at which the position information ofthe movable portion of the first variable capacitor 21 is “0”, and theposition information of the movable portion of the second variablecapacitor 24 is “0”). Similarly, T(100,0) indicates the T-parametermeasured after adjusting the impedance adjustment apparatus 3P to animpedance adjustment position (100,0) (adjustment position at which theposition information of the movable portion of the first variablecapacitor 21 is “100”, and the position information of the movableportion of the second variable capacitor 24 is “0”). Other T-parametersare displayed with a similar approach. Note that although T-parametersare measured for all 10201 impedance adjustment positions of theimpedance adjustment apparatus 3P, some of those values have beenabbreviated as “ . . . ” in Table 1 in order to simplify thedescription.

Here, the S-parameters and the T-parameters will be described.

The S-parameters are parameters indicating the transmissioncharacteristics of a prescribed four-terminal network (also known as a“two-port network”) at the time when a high frequency signal is inputafter connecting lines having characteristic impedance (e.g., 50Ω) toinput and output terminals of the four-terminal network as is wellknown. The S-parameters are, as shown in Equation 1, represented as amatrix that is constituted by elements consisting of an input-sidevoltage reflection coefficient (S₁₁), a transmission coefficient (S₂₁)of a forward voltage, a transmission coefficient (S₁₂) of a reversevoltage, and an output-side voltage reflection coefficient (S₂₂)

$\begin{matrix}\begin{bmatrix}S_{11} & S_{12} \\S_{21} & S_{22}\end{bmatrix} & \left\langle {{Equation}\mspace{14mu} 1} \right\rangle\end{matrix}$

The T-parameters are, as shown in Equation 2, parameters that can beconverted from the S-parameters. In measuring the transmissioncharacteristics of a four-terminal network, the S-parameters aregenerally simple to measure, but the T-parameters are simple to use whenperforming calculations.

$\begin{matrix}\left. {\frac{1}{S_{12}}\begin{bmatrix}{{S_{12} \cdot S_{21}} - {S_{11} \cdot S_{22}}} & S_{22} \\{- S_{11}} & 1\end{bmatrix}}\rightarrow\begin{bmatrix}T_{11} & T_{12} \\T_{21} & T_{22}\end{bmatrix} \right. & \left\langle {{Equation}\mspace{14mu} 2} \right\rangle\end{matrix}$

In the four-terminal network shown in FIG. 10, the S-parameters aredefined as in Equation 3 and the T-parameters are as defined as inEquation 4.

$\begin{matrix}{\begin{bmatrix}b_{1} \\b_{2}\end{bmatrix} = {\begin{bmatrix}S_{11} & S_{12} \\S_{21} & S_{22}\end{bmatrix}\begin{bmatrix}a_{1} \\a_{2}\end{bmatrix}}} & \left\langle {{Equation}\mspace{14mu} 3} \right\rangle \\{\begin{bmatrix}b_{2} \\a_{2}\end{bmatrix} = {\begin{bmatrix}T_{11} & T_{12} \\T_{21} & T_{22}\end{bmatrix}\begin{bmatrix}a_{1} \\b_{1}\end{bmatrix}}} & \left\langle {{Equation}\mspace{14mu} 4} \right\rangle\end{matrix}$

In FIG. 10, the relationship between an input reflection coefficient Γin(input-end reflection coefficient) and an output reflection coefficientΓout (output-end reflection coefficient) when a port 1 is the input sideand a port 2 is the load side can be represented using the S-parameters(see Eq. 5) or the T-parameters (see Eq. 6).

$\begin{matrix}\begin{matrix}{{\Gamma\;{out}} = \frac{a_{2}}{b_{2}}} \\{= \frac{{\Gamma\;{in}} - S_{11}}{{S_{12} \cdot S_{21}} + {S_{22}\left( {{\Gamma\;{in}} - S_{11}} \right)}}}\end{matrix} & \left\langle {{Equation}\mspace{14mu} 5} \right\rangle \\\begin{matrix}{{\Gamma\;{out}} = \frac{a_{2}}{b_{2}}} \\{= \frac{T_{21} + {{T_{22} \cdot \Gamma}\;{in}}}{T_{11} + {{T_{12} \cdot \Gamma}\;{in}}}}\end{matrix} & \left\langle {{Equation}\mspace{14mu} 6} \right\rangle\end{matrix}$

As described above, in the high frequency power supply system shown inFIG. 9, the output frequency of the high frequency power source 1 p isfixed to a certain constant frequency. However, for example, in PatentDocument 2 (JP 2006-310245), technology is proposed for performingimpedance matching while adjusting the output frequency of the highfrequency power source, focusing on the change in the load-sideimpedance seen from the output end of the high frequency power source tothe load side when the output frequency of the high frequency powersource is changed. With the technology described in Patent Document 2,impedance matching is performed by changing the output frequency of thehigh frequency power source to change the load-side impedance, becausethe capacitance component and the inductance component that are includedin the load-side impedance change depending on the frequency. Note that,in the present specification, a high frequency power source whose outputfrequency can be adjusted (changed) in this way is called a highfrequency power source 1 v employing a variable frequency system.

Also, even in the case where a high frequency power source 1 v employinga variable frequency system is used, an impedance adjustment apparatusthat includes an adjustment circuit 20 shown in FIG. 11 is used in somecases, as described in Patent Document 3 (JP 2008-181846). Theadjustment circuit 20 is an adjustment circuit in which the secondvariable capacitor 24 is replaced by a capacitor 22 having a fixedcapacitance in the adjustment circuit 20 p shown in FIG. 9. With theimpedance adjustment apparatus described in Patent Document 3, impedancematching is performed by adjusting the output frequency of the highfrequency power source 1 v together with adjusting the position of themovable portion of the first variable capacitor 21. Note that becausethe capacitance of the capacitor 22 of the adjustment circuit 20 isfixed, an adjustment unit for adjusting capacitance and a positiondetection unit for detecting position information of the movable portionare not provided.

With the impedance matching method described in Patent Document 1 thatperforms impedance matching using characteristic parameters measured inadvance, because of the characteristic parameters being measured withrespect to a single output frequency, cases occur where impedancematching cannot be performed when the impedance matching methoddescribed in Patent Document 1 is applied to the high frequency powersupply system described in Patent Document 2 or Patent Document 3 whilechanging the output frequency of the high frequency power source 1 v.

SUMMARY OF THE INVENTION

The present invention was conceived under the above circumstances. Inview of this, the present invention has an object to provide animpedance adjustment apparatus that is able to perform impedancematching using characteristic parameters, even in the case where anoutput frequency is adjusted (changed) using a high frequency powersource employing a variable frequency system.

An impedance adjustment apparatus provided based on an embodiment of thepresent invention is provided between a high frequency power source anda load, and is configured to adjust impedance seen from the highfrequency power source to the load.

The impedance adjustment apparatus includes an input end for connectingto the high frequency power source, an output end for connecting to theload, and a variable electrical characteristic element. The impedanceadjustment apparatus is further provided with a characteristic parameterstorage unit for storing a plurality of characteristic parametersindicating transmission characteristics of the impedance adjustmentapparatus, the plurality of characteristic parameters being parametersthat are respectively acquired for a plurality of adjustment points atwhich a plurality of frequency adjustment points that correspond tooutput frequencies of the high frequency power source are combined witha plurality of electrical characteristic adjustment points thatcorrespond to electrical characteristics of the variable electricalcharacteristic element; a high frequency information detection unit fordetecting high frequency information of the input end; an outputfrequency acquisition unit for acquiring an output frequency of the highfrequency power source; an electrical characteristic acquisition unitfor acquiring an electrical characteristic of the variable electricalcharacteristic element; a characteristic parameter acquisition unit foracquiring a characteristic parameter for an adjustment point at whichthe acquired output frequency is combined with the acquired electricalcharacteristic, based on the plurality of characteristic parameters; anoutput reflection coefficient calculation unit for calculating an outputreflection coefficient of the output end, based on the high frequencyinformation detected by the high frequency information detection unitand the characteristic parameter acquired by the characteristicparameter acquisition unit; a specifying unit for specifying animpedance adjustment point at which to match the target impedance to theimpedance of the high frequency power source, among the plurality ofadjustment points, based on the output reflection coefficient, a targetinput reflection coefficient set in advance, and the plurality ofcharacteristic parameters; an electrical characteristic elementadjustment unit for adjusting the electrical characteristic of thevariable electrical characteristic element to an electricalcharacteristic of the impedance adjustment point; and a command signaloutput unit for outputting, to the high frequency power source, acommand signal for adjusting the output frequency of the high frequencypower source to an output frequency of the impedance adjustment point.

Preferably, the characteristic parameter storage unit storescharacteristic parameters measured for every adjustment point, orcharacteristic parameters that are converted from the measuredcharacteristic parameters and are different in type from the measuredcharacteristic parameters.

Preferably, the measured characteristic parameters are S-parameters andthe characteristic parameters that are different in type from themeasured characteristic parameters are T-parameters.

Preferably, the plurality of characteristic parameters that are storedin the characteristic parameter storage unit include actual valuesmeasured at each adjustment point with respect to a portion of theplurality of adjustment points, and estimated values computed at eachadjustment point by interpolation using the actual values with respectto adjustment points that have not been measured among the plurality ofadjustment points.

Preferably, the adjustment points at which the characteristic parameterswere measured are adjustment points at which a portion of frequencyadjustment points extracted at a first interval from the plurality offrequency adjustment points are combined with a portion of electricalcharacteristic adjustment points extracted at a second interval from theplurality of electrical characteristic adjustment points.

Preferably, the specifying unit, based on the target input reflectioncoefficient and the plurality of characteristic parameters, calculates avirtual output reflection coefficient of the output end at eachadjustment point assuming that the output frequency of the highfrequency power source and the electrical characteristic of the variableelectrical characteristic element have been adjusted to the plurality ofadjustment points, and specifies an adjustment point at which adifference between the output reflection coefficient and the virtualoutput reflection coefficient is smallest as an adjustment point of thetarget impedance.

Preferably, the high frequency information is a traveling wave voltagethat travels from the high frequency power source to the load and areflected wave voltage that is reflected from the load to the highfrequency power source.

Preferably, the output reflection coefficient calculation unitcalculates an input reflection coefficient of the input end based on thehigh frequency information, and calculates the output reflectioncoefficient based on the calculated input reflection coefficient and theacquired characteristic parameter.

Preferably, the impedance adjustment apparatus is further provided witha frequency detection unit for detecting the output frequency of thehigh frequency power source using the high frequency information.

Preferably, the high frequency power source outputs, to the impedanceadjustment apparatus, information on an output frequency of a highfrequency wave that is output, and the output frequency acquisition unitacquires the information on the output frequency that is input from thehigh frequency power source, as the output frequency of the highfrequency power source.

According to the present invention, an impedance adjustment apparatusthat is able to perform impedance matching using characteristicparameters, even in the case where an output frequency is adjusted(changed) using a high frequency power source employing a variablefrequency system, can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an exemplary configuration of a highfrequency power supply system to which an impedance adjustment apparatusthat is based on an embodiment of the present invention is applied.

FIG. 2 is a diagram showing an example of S-parameters or T-parametersstored in the memory.

FIG. 3 is a diagram for illustrating a method of using linearinterpolation to derive S-parameters that have not been measured.

FIG. 4 is an example in a case of measuring the S-parameters in a grid,and measuring the S-parameters with respect to combination informationof another portion.

FIG. 5 is a diagram showing a configuration of a measurement circuit formeasuring S-parameters of the impedance adjustment apparatus.

FIG. 6 is a functional block diagram of a control unit.

FIG. 7 is a diagram showing an example of a way of changing of avariable that is used in order to specify target combinationinformation.

FIG. 8 is a diagram showing an exemplary configuration of a highfrequency power supply system.

FIG. 9 is a block diagram showing an exemplary configuration of a highfrequency power supply system that includes a conventional impedanceadjustment apparatus.

FIG. 10 is a concept diagram of a four-terminal network.

FIG. 11 is a diagram showing an example of an adjustment circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings. Note that the same signs aregiven to configuration that is the same as or similar to theconventional configuration shown in FIG. 9.

FIG. 1 is a block diagram showing an exemplary configuration of a highfrequency power supply system to which an impedance adjustment apparatus3A that is based on an embodiment of the present invention is applied.

The high frequency power supply system is a system that performs aprocessing process such as plasma etching, for example, on a workpiecesuch as a semiconductor wafer or a liquid crystal substrate. The highfrequency power supply system is constituted by a high frequency powersource 1 v employing a variable frequency system, a transmission line 2,an impedance adjustment apparatus 3A, a load connecting portion 4, and aload 5 consisting of a plasma processing apparatus. Note that, in thepresent specification, a system that combines the high frequency powersource 1 v and the impedance adjustment apparatus 3A is a high frequencywave matching system.

The high frequency power source 1 v is connected to an input end 301 ofthe impedance adjustment apparatus 3A via the transmission line 2, whichconsists of a coaxial cable, for example, and the load 5 is connected toan output end 302 via the load connecting portion 4. The load connectingportion 4 is covered with copper plate, in order to suppress leakage ofelectromagnetic waves.

The high frequency power source 1 v is an apparatus that supplies highfrequency power to the load 5. The output frequency of the highfrequency power source 1 v is a frequency in a wireless frequency band.A frequency in a wireless frequency band is generally a frequency inhundreds of kilohertz or tens of megahertz, with the output frequency ofthe high frequency power source 1 v being a frequency such as 400 kHz, 2MHz, 13.56 MHz or 50 MHz, for example. Note that the output frequency ofthe high frequency power source 1 v is the frequency of a fundamentalwave.

The output frequency of the high frequency power source 1 v ischangeable in a predetermined range. The variable range of the outputfrequency is set as appropriate in consideration of factors such as theperformance of an oscillator (not shown) that is provided in the highfrequency power source 1 v. For example, in the case where the centerfrequency of the variable range is 2 MHz, the variable range of theoutput frequency is designed in a range of 2 MHz±10% (1.8-2.2 MHz).

Also, the output frequency is designed to be changed stepwise over 101steps from “0” to “100”, where “0” is the lower limit frequency of thevariable range of the output frequency, and “100” is the upper limitfrequency of the variable range of the output frequency, for example.Because the “0” step is 1.8 MHz and the “100” step is 2.2 MHz in thecase where the variable range of the output frequency is 2 MHz±10%(1.8-2.2 MHz), the output frequency of the high frequency power source 1v is changed stepwise at a pitch of 0.004 MHz (4 kHz) in a range from1.8 to 2.2 MHz.

It should be obvious that the output frequency and the variable range ofthe output frequency are not limited to the above. For example, theoutput frequency may also be set to a high output frequency of severalhundred MHz. Also, the variable range of the output frequency may alsobe designed in a range of 2 MHz±5% (1.9-2.1).

The high frequency power source 1 v recognizes the output frequency, andoutputs information on the output frequency to the impedance adjustmentapparatus 3A as power source recognition output frequency informationF_(ge). The power source recognition output frequency information F_(ge)output from the high frequency power source 1 v is input to a controlunit 100 of the impedance adjustment apparatus 3A discussed later. Also,as discussed later, target output frequency information F_(mat) that isused for impedance matching is input to the high frequency power source1 v from the control unit 100 of the impedance adjustment apparatus 3A.The high frequency power source 1 v changes the output frequency basedon the target output frequency information F_(mat) that is input fromthe control unit 100.

The load 5 is a plasma processing apparatus for processing a workpiecesuch as a semiconductor wafer or a liquid crystal substrate, using amethod such as etching or CVD. In the plasma processing apparatus,various types of processing processes are executed according to thepurpose of processing the workpiece. For example, in the case of etchingthe workpiece, a processing process in which the type of gas appropriatefor the etching, the gas pressure, the power supply value of highfrequency power, the supply duration of high frequency power and thelike are suitably set is performed. In the plasma processing apparatus,the workpiece is placed within a chamber (not shown) in which a plasmadischarge gas is enclosed. The plasma discharge gas is then changed froma non-plasma state to a plasma state by supplying high frequency powerfrom the high frequency power source 1 v to a pair of electrodes withinthe chamber (not shown), and the workpiece is processed using the gasthat is in a plasma state.

The impedance adjustment apparatus 3A matches the impedance of the highfrequency power source 1 v and the impedance of the load 5. Morespecifically, in the case where the output impedance of the highfrequency power source 1 v is designed to 50Ω, and the high frequencypower source 1 v is connected to the input end 301 of the impedanceadjustment apparatus 3A with a transmission line 2 having acharacteristic impedance of 50 ohm, the impedance adjustment apparatus3A adjusts the impedance seen from the input end 301 of the impedanceadjustment apparatus 3A to the load 5 side to a value approaching 50Ω.This adjustment results in the load-side impedance ZL seen from theoutput end of the high frequency power source 1 v to the load 5 sidebeing adjusted to a value approaching 50 Ω.

Note that although the characteristic impedance is 50Ω in the presentembodiment, the characteristic impedance is not limited to 50Ω. Also, itis desirable to set the input reflection coefficient Γin of the inputend 301 of the impedance adjustment apparatus 3A to 0, that is, to matchthe load-side impedance ZL to the characteristic impedance. However,because the impedances can normally be regarded as matched if the inputreflection coefficient Γin is less than or equal to a predeterminedtolerance value, in the present embodiment the impedance adjustmentapparatus 3A adjusts the load-side impedance ZL such that inputreflection coefficient Γin will be less than or equal to thepredetermined tolerance value.

The impedance adjustment apparatus 3A is provided with a directionalcoupler 10, the control unit 100, an adjustment circuit 20, anadjustment unit 30, a position detection unit 40, and a memory 70. Also,the adjustment circuit 20 is provided with a variable capacitor 21, acapacitor 22 having a fixed impedance, and an inductor 23. The variablecapacitor 21 is substantially the same variable capacitor as the firstvariable capacitor 21 in FIG. 9. The impedance adjustment apparatus 3Aperforms impedance matching by adjusting both the position of themovable portion (movable electrode) of the variable capacitor 21provided in the adjustment circuit 20 and the output frequency of thehigh frequency power source 1 v. A detailed description of the impedancematching operation of the impedance adjustment apparatus 3A will begiven later.

Note that, as described above, because the position information of themovable portion of the variable capacitor 21 can be treated asinformation representing capacitance (capacitance information), thisposition information is treated as information representing theelectrical characteristics of the variable capacitor 21 (electricalcharacteristic information).

The adjustment circuit 20 is not limited to the configuration shown inFIG. 1, and may have another configuration. For example, although theadjustment circuit 20 shown in FIG. 1 is generally called an L-typecircuit, a known adjustment circuit such as a n-type circuit can beused. The type of circuit that is used is determined by factors such asthe output frequency of the high frequency power source 1 v andconditions of the load 5.

The directional coupler 10 separates and detects a high frequency wavethat travels from the high frequency power source 1 v to the load 5 side(hereinafter, traveling wave) and a high frequency wave reflected fromthe load 5 side (hereinafter, reflected wave). The directional coupler10 outputs the detected traveling wave and reflected wave respectivelyat a traveling voltage and a reflected wave voltage. The directionalcoupler 10 has one input port 11 and three output ports 12, 13 and 14.The high frequency power source 1 v is connected to the input port 11,and the adjustment circuit 20 is connected to the first output port 12.Also, the second output port 13 and the third output port 14 areconnected to the control unit 100.

Note that the directional coupler 10 functions as a portion of a highfrequency information detection unit of the present invention. Also, acombination of the directional coupler 10 and a vectorization unit 110discussed later is an example of the high frequency informationdetection unit of the present invention.

The traveling wave that is input to the directional coupler 10 from theinput port 11 is output from the first output port 12 and the secondoutput port 13. The traveling wave that is output from the first outputport 12 is input to the adjustment circuit 20. The reflected wave thatis reflected by the adjustment circuit 20 and input to the directionalcoupler 10 from the first output port 12 is output from the input port11 and the third output port 14. The traveling wave that is output fromthe second output port 13 and the reflected wave that is output from thethird output port 14 are input to the control unit 100 after beingattenuated to a suitable level by an attenuator (not shown).

Note that a high frequency detector can be used instead of thedirectional coupler 10. The high frequency detector detects highfrequency voltage and high frequency current that are input from thehigh frequency power source 1 v to the input end 301, and a phasedifference thereof (phase difference between the high frequency voltageand high frequency current), for example. The high frequency voltage,the high frequency current and the phase difference detected by the highfrequency detector are input to the control unit 100.

The control unit 100 serves as a control center of the impedanceadjustment apparatus 3A. The control unit 100 has a CPU, a memory, a ROMand the like not shown. The control unit 100 can also be constitutedusing a gate array that can appropriately define and change a logiccircuit provided therein, such as FPGA (Field Programmable Gate Array),for example. The control unit 100 changes the capacitance of thevariable capacitor 21 and the output frequency of the high frequencypower source 1 v to adjust the impedance of the adjustment circuit 20,based on the traveling wave voltage and reflected wave voltage that areoutput from the directional coupler 10.

The adjustment unit 30 is connected to the movable portion (movableelectrode) of the variable capacitor 21. The adjustment unit 30 is adrive means for displacing the position of the movable portion of thevariable capacitor 21. The adjustment unit 30 is constituted by astepping motor, a motor drive circuit and the like (all not shown), forexample. The motor drive circuit provided in the adjustment unit 30drives the stepping motor based on a command signal that is input fromthe control unit 100, and displaces the position of the movable portionof the variable capacitor 21. In the present embodiment, the capacitanceof the variable capacitor 21 can be adjusted over 101 steps, forexample. The control unit 100 adjusts the capacitance of the variablecapacitor 21 stepwise by controlling the amount of rotation of thestepping motor provided in the adjustment unit 30. Note that theadjustment unit 30 is an example of an electrical characteristic elementadjustment unit of the present invention.

The position detection unit 40 that detects the position of the movableportion that is adjusted by the adjustment unit 30 is provided in thevariable capacitor 21. Position information of the movable portion ofthe variable capacitor 21 detected by the position detection unit 40 isinput to the control unit 100. The control unit 100 recognizes theposition of the movable portion of the variable capacitor 21 based onthis position information. Note that the position detection unit 40 isan example of an electrical characteristic acquisition unit of thepresent invention.

The memory 70 is connected to the control unit 100. Characteristicparameters of the impedance adjustment apparatus 3A measured in advanceare stored in the memory 70. The characteristic parameters areS-parameters indicating the transmission characteristics in the casewhere the entire impedance adjustment apparatus 3A is regarded as atransmission apparatus or T-parameters converted from the S-parameters.The characteristic parameters stored in the memory 70 are the measuredvalues of S-parameters measured after setting the position (capacitance)of the movable portion of the variable capacitor 21 to a position set asa measurement target and inputting a high frequency wave of thefrequency set as a measurement target to the impedance adjustmentapparatus 3A, or T-parameters converted from the measured values of theS-parameters. The positions of the movable portion and the frequenciesof the high frequency wave serving as measurement targets are thevariable positions of the movable portion of the variable capacitor 21and the output frequencies of the high frequency power source 1 v thatare included in a portion of combinations extracted from among allcombinations of the stepwise variable positions of the movable portionof the variable capacitor 21 and the stepwise change values of theoutput frequency of the high frequency power source 1 v. Note that thememory 70 is an example of a characteristic parameter storage unit ofthe present invention.

In the present embodiment, position information of the movable portionof the variable capacitor 21 is represented with a variable C, outputfrequency information of the high frequency power source 1 v isrepresented with a variable F, and combination information of theposition of the movable portion of the variable capacitor 21 and theoutput frequency of the high frequency power source 1 v is representedin coordinate form such as (C,F). In the above example, “C” changesstepwise over a range of 0 to 100 (101 steps), and “F” changes stepwiseover a range of 0 to 100 (101 steps). Accordingly, in the presentembodiment, there are (101×101=) 10201 sets of combination information(C,F). It should be obvious that a configuration may be adopted in whichthe variable C and the variable F change over other ranges.

Table 2 shows an example in which S-parameters are stored in the memory70 as characteristic parameters, and Table 3 shows an example in whichT-parameters are stored in the memory 70 as characteristic parameters.

TABLE 2 C 0 10 20 . . . . . . 80 90 100 F 0 S (0, 0)  S (10, 0)  S (20,0)  . . . . . . S (80, 0)  S (90, 0)  S (100, 0)  10 S (0, 10) S (10,10) S (20, 10) . . . . . . S (80, 10) S (90, 10) S (100, 10) 20 S (0,20) S (10, 20) S (20, 20) . . . . . . S (80, 20) S (90, 20) S (100, 20). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . 80 S (0, 80) S (10, 80) S (20, 80) .. . . . . S (80, 80) S (90, 80) S (100, 80) 90 S (0, 90) S (10, 90) S(20, 90) . . . . . . S (80, 90) S (90, 90) S (100, 90) 100  S (0, 100) S (10, 100)  S (20, 100) . . . . . .  S (80, 100)  S (90, 100)  S (100,100)

TABLE 3 C 0 10 20 . . . . . . 80 90 100 F 0 T (0, 0)  T (10, 0)  T (20,0)  . . . . . . T (80, 0)  T (90, 0)  T (100, 0)  10 T (0, 10) T (10,10) T (20, 10) . . . . . . T (80, 10) T (90, 10) T (100, 10) 20 T (0,20) T (10, 20) T (20, 20) . . . . . . T (80, 20) T (90, 20) T (100, 20). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . 80 T (0, 80) T (10, 80) T (20, 90) .. . . . . T (80, 80) T (90, 80) T (100, 80) 90 T (0, 90) T (10, 90) T(20, 90) . . . . . . T (80, 90) T (90, 90) T (100, 90) 100  T (0, 100) T (10, 100)  T (20, 100) . . . . . .  T (80, 100)  T (90, 100)  T (100,100)

The S-parameters shown in Table 2 were obtained by measuring theS-parameters of the impedance adjustment apparatus 3A while changing theposition of the movable portion of the variable capacitor 21 and thefrequency of the high frequency wave that is input to the impedanceadjustment apparatus 3A to values corresponding to each set ofcombination information (C,F) serving as a measurement target, using 121sets of combination information (C,F) combining 11 variables C obtainedby changing the range of 0 to 100 over 10 steps and 11 variables Fobtained by changing the range of 0 to 100 over 10 steps as measurementtargets.

Note that since combination information (C,F) denotes combinationinformation of position information C of the movable portion of thevariable capacitor 21 and output frequency information F of the highfrequency power source 1 v, the corresponding position of the movableportion of the variable capacitor 21 and output frequency of the highfrequency power source 1 v will be known if this combination informationis known. That is, the capacitance information of the variable capacitor21 (electrical characteristic information) and the output frequency ofthe high frequency power source 1 v will be known. For this reason,rather than simply storing the S-parameters or the T-parameters in thememory 70, the S-parameters or the T-parameters are stored inassociation with the combination information (C,F) of the position ofthe movable portion of the variable capacitor 21 and the outputfrequency of the high frequency power source 1 v.

In Table 2, S(C,F) shows the S-parameter of the impedance adjustmentapparatus 3A measured after setting the position of the movable portionof the variable capacitor 21 to a position corresponding to “C” andsetting the frequency of the high frequency wave that is input to theimpedance adjustment apparatus 3A to a frequency corresponding to “F”.For example, S(0,0) indicates the S-parameter measured after setting theposition of the movable portion of the variable capacitor 21 to aposition corresponding to C=0 and setting the frequency of the highfrequency wave that is input to the impedance adjustment apparatus 3A toa frequency corresponding to F=0. Similarly, S(100,0) shows theS-parameter measured after setting the position of the movable portionof the variable capacitor 21 to a position corresponding to C=100 andsetting the frequency of the high frequency wave that is input to theimpedance adjustment apparatus 3A to a frequency corresponding to F=0.

The T-parameters shown in Table 3 are obtained by converting themeasured values of the S-parameters shown in Table 2 into theT-parameters using the conversion equation shown in Equation 2. TheT-parameters are stored in the memory 70 in association with thecombination information (C,F) of the position of the movable portion ofthe variable capacitor 21 and the output frequency of the high frequencypower source 1 v.

Accordingly, T(C,F) in Table 3 shows the T-parameter measured aftersetting the position of the movable portion of the variable capacitor 21to a position corresponding to “C” and setting the output frequency ofthe high frequency power source 1 v to a frequency corresponding to “F”.For example, T(0,0) shows the T-parameter measured after setting theposition of the movable portion of the variable capacitor 21 to aposition corresponding to C=0 and setting the output frequency of thehigh frequency power source 1 v to a frequency corresponding to F=0.Similarly, T(100,0) shows the T-parameter measured after setting theposition of the movable portion of the variable capacitor 21 to aposition corresponding to C=100 and setting the output frequency of thehigh frequency power source 1 v to a frequency corresponding to F=0.

FIG. 2 illustrates, as coordinates (C,F), combinations of the positioninformation of the movable portion of the variable capacitor 21 and theoutput frequency information of the high frequency power source 1 v usedto measure the S-parameters or the T-parameters that are stored in thememory 70. In FIG. 2, the horizontal axis is the position information Cof the movable portion of the variable capacitor 21, and the verticalaxis is the output frequency information F of the high frequency powersource 1 v. Also, the black dots indicate the positions of the sets ofcombination information (C,F) where the S-parameters or the T-parameterswere measured. As shown in FIG. 2, the S-parameters or the T-parametersof the impedance adjustment apparatus 3A are not measured for allcombinations of the variable numbers of the movable portion of thevariable capacitor 21 and the variable numbers of the output frequencyof the high frequency power source 1 v but rather for a portion ofcombinations.

As described above, although the S-parameters are simple to measure inthe measurement of transmission characteristics, the T-parameters aresimple to use in calculations performed in impedance matching, and thus,usually, values obtained by converting S-parameters into T-parametersare stored in the memory 70. In the case where S-parameters are storedin the memory 70, the S-parameters are read from the memory 70 whenperforming impedance matching, and converted into T-parameters for usein calculations. However, because operation load increases whenprocessing for converting the S-parameters into the T-parameters isperformed at the time of impedance matching, it is more preferable tostore the T-parameters in the memory 70 in advance. In the followingdescription, it is assumed that T-parameters are stored in the memory 70and impedance matching is performed using those T-parameters.

It is preferable, from the viewpoint of accuracy, to measure theS-parameters for all combinations of the values that can be taken by theposition of the movable portion of the variable capacitor 21 and thevalues that can be taken by the output frequency of the high frequencypower source 1 v. However, many measurement man hours would be required,because the amount of measurement would be considerable when measuringthe S-parameters for all combinations. In the present embodiment, inorder to ease the calculation load, rather than measuring theS-parameters for all combinations, S-parameters are measured for aportion of combinations, and the S-parameters that have not beenmeasured are interpolated through performing interpolation by linearapproximation using the measured values. As the method of interpolation,bi-linear interpolation is used, for example. The same applies to theT-parameters converted from the S-parameters.

The method of deriving the S-parameters that have not been measured bylinear interpolation will be described using FIG. 3.

In the following description, an element S₁₁ of the S-parameters istaken as an example. Also, the elements of the S-parameters arerepresented by “element names (S₁₁, etc.) of the S-parameters” and“combination information (C,F)”. For example, the element S₁₁ ofS(10,10) is represented as S₁₁(10,10), the element S₁₁ of S(10,20) isrepresented as S₁₁(10,20), the element S₁₁ of S(20,10) is represented asS₁₁(20,10) and the element S₁₁ of S(20,20) is represented as S₁₁(20,20).Accordingly, in FIG. 3, the measured value of S₁₁(10,10) is shown asbeing 100, the measured value of S₁₁(10,20) is shown as being 170, themeasured value of S₁₁(20,10) is shown as being 160, and the measuredvalue of S₁₁(20,20) is shown as being 200. Note that each value ofelement S₁₁ shown in FIG. 3 is not an actual measured value but anexemplary numerical value for illustrating linear interpolation.

For example, an element S₁₁(18,16) of the S-parameter for thecombination information (C,F)=(18,16) that has not been measured isderived by the interpolation operations of the following first to thirdsteps.

First step: Derive an estimated value of S₁₁(18,10) by interpolation,using the measured value 100 of S₁₁(10,10) and the measured value 160 ofS₁₁(20,10).

Second step: Derive an estimated value of S₁₁(18,20) by interpolation,using the measured value 170 of S₁₁(10,20) and the measured value 200 ofS₁₁(20,20).

Third step: Derive an estimated value of S₁₁(18,16) by interpolation,using the estimated value of S₁₁(18,10) and the estimated value ofS₁₁(18,20) derived at the first step and the second step.

Specifically, the interpolation operation of each step is as follows.

Estimated value of S₁₁(18,10): 100×0.2+160×0.8=148

Estimated value of S₁₁(18,20): 170×0.2+200×0.8=194

Estimated value of S₁₁(18,16): 148×0.4+194×0.6=175.6

Accordingly, the estimated value of S₁₁(18,16) is 175.6.

The estimated values of the other elements S₁₂(18,16), S₂₁(18,16) andS₂₂(18,16) can also be respectively derived by similar calculations.

Because S-parameters are usually measured after setting a portion ofcombination information sets (C,F) extracted in a grid as measurementtargets, among all sets of combination information (C,F), as shown inFIG. 3, in the case where the combination information (C,F) for derivingan S-parameter by interpolation is in an area surrounded by four sets ofcombination information (C,F) that have been measured, four S-parametersthat have been measured are used in the interpolation operation, as inthe above example. In the case where the combination information (C,F)for deriving the S-parameter is between two sets of combinationinformation (C,F) that have been measured, the calculation is easybecause the S-parameter of that combination information (C,F) can beinterpolated using the two S-parameters that have been measured.

When measurement targets are extracted in a grid as shown in Table 2,there is an advantage in that the interpolation operation for derivingthe S-parameters of combination information (C,F) for which measurementhas not been performed is easily performed. It should be obvious thatthe interpolation operation can be performed even when the sets ofcombination information (C,F) for which S-parameters have been measuredare not in a grid.

Although S-parameters were measured for a portion of combinationinformation sets (C,F) extracted in a grid, among all sets ofcombination information (C,F), in the example in Table 2, S-parametersmay also be measured for another portion of combination information sets(C,F), in addition to the portion of combination information sets (C,F)extracted in a grid, as shown in FIG. 4.

In FIG. 4, the horizontal axis is the position information C of themovable portion of the variable capacitor 21, and the vertical axis isthe output frequency information F of the high frequency power source 1v. FIG. 4 shows an example in which S-parameters are also measured forcombination information sets (C,F) included to an area A and an area Bin addition to the combination information sets (C,F) that are indicatedby the black dots.

For example, in the case where the combination information sets (C,F)that are expected to be used in impedance matching are known, it isfavorable to measure the S-parameters for all sets of combinationinformation (C,F) that are included in a predetermined range that isbased on those combination information sets (C,F). In this way,measuring S-parameters for combination information sets (C,F) that aresubstantively required enables accurate impedance matching to beperformed, while suppressing any increase in man hours or memorycapacity for measuring S-parameters.

Also, although the four S-parameters [S(10,10)], [S(20,10)], [S(10,20)]and [S(20,20)] surrounding the S-parameter [S(18,16)] that is to beestimated are used, among the measured S-parameters, to calculate theestimated value of the S-parameter [S(18,16)] in the example in FIG. 3,the four S-parameters that are used in the calculations are not limitedto these parameters. For example, the estimated value of the S-parameter[S(18,16)] may be interpolated using the four S-parameters, [S(0,0)],[S(30,0)], [S(0,30)] and [S(30,30)]. Because the accuracy of theestimated value is thought to deteriorate as the distance between theS-parameter that is to be estimated and the measured S-parameters thatare used in the interpolation operation increases, the S-parameters tobe used in the interpolation operation need to be appropriatelydetermined with consideration for accuracy and convenience.

Because S-parameters that have not been measured can be estimated byinterpolation from S-parameters measured in advance as described above,the estimated values of S-parameters may be derived by interpolation forcombination information sets (C,F) for which the S-parameter has notbeen measured, among all sets of combination information (C,F), and boththe measured values and the estimated values of the S-parameters maystored in advance in the memory 70 in association with the combinationinformation sets (C,F). In this case, estimated values may be derivedfor all sets of combination information (C,F) for which measurement hasnot been performed, or estimated values may be derived for only aportion of combination information sets (C,F) among all sets ofcombination information (C,F) for which measurement has not beenperformed. Also, T-parameters converted from the S-parameters using theconversion equation of Equation 2 may be stored in the memory 70. Notethat when the estimated values of S-parameters or the estimated valuesof T-parameters converted from the estimated values of S-parameters arestored in the memory 70, the calculation load when impedance matching isperformed can be reduced but a large memory capacity is required, andthus an appropriate selection should be made according to the actualsituation.

As described above, in the case of storing the estimated values ofS-parameters or the estimated values of T-parameters converted from theestimated values of S-parameters in the memory 70, a configuration maybe adopted in which measured S-parameters or T-parameters converted frommeasured S-parameters are stored in a first storage area within thememory 70, and the estimated values of S-parameters or the estimatedvalues of T-parameters converted from the estimated values ofS-parameters are stored in an second storage area within the memory 70,for example.

It should be obvious that the first storage area and second storage areamay be provided in the same hardware or may be provided in differenthardware. Also, in the case where the first storage area and the secondstorage area are provided in the same hardware, a configuration may beadopted in which the first storage area and second storage area aredivided into areas of predetermined capacity or are not divided. Notethat it is preferable to adopt a configuration in which it can bedistinguished whether S-parameters or T-parameters that are stored aremeasured S-parameters or T-parameters converted from measuredS-parameters, or whether they are estimated values of S-parameters orestimated values of T-parameters converted from estimated values ofS-parameters.

Although an example in which S-parameters are interpolated was describedabove, T-parameters corresponding to S-parameters that have not beenmeasured can be estimated by linear interpolation, using T-parametersconverted from measured S-parameters. The interpolation method issimilar to the above case of S-parameters.

Note that in the case where measured S-parameters are converted intoT-parameters, T-parameters corresponding to combination information sets(C,F) for which the S-parameter has not been measured can be derived byinterpolation in the following manner.

That is, as shown in FIG. 2, the data interval on the variable C axis ofmeasured S-parameters (T-parameters) is given as c₀ (in the FIG. 2example, c₀=10), and the data interval on the variable F axis is givenas f₀ (in the FIG. 2 example, f₀=10). Also, the integer portion andfractional portion of C/c₀ are given respectively as n_(c) and d_(c),the integer portion and fractional portion of F/f₀ are givenrespectively as n_(f) and d_(f).

For example, if the position of the movable portion of the variablecapacitor 21 is “83”, and the data interval c₀ is “10”, n_(c)=8 andd_(c)=0.3.

In this case, the elements T₁₁, T₁₂, T₂₁ and T₂₂ constitutingT-parameters converted from S-parameters are represented as in Equation7.

$\begin{matrix}{{T_{11} = {{T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\left\{ {{T_{11}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\} d_{c}} + {\left\{ {{T_{11}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\} d_{f}} + {\left\{ {{T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{11}\left\lbrack {{\left( {n_{c} + 1} \right)c_{1}},{n_{f}f_{0}}} \right\rbrack} - {T_{11}\left\lbrack {{n_{c}c_{1}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{11}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack}} \right\} d_{c}d_{f}}}}{T_{12} = {{T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\left\{ {{T_{12}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\} d_{c}} + {\left\{ {{T_{12}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\} d_{f}} + {\left\{ {{T_{12}\left( {{n_{c}c_{0}},{n_{2}f_{0}}} \right)} - {T_{12}\left\lbrack {{\left( {n_{c} + 1} \right)c_{1}},{n_{f}f_{0}}} \right\rbrack} - {T_{12}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{12}\left\lbrack {{\left( {n_{c} + 1} \right)c_{1}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack}} \right\} d_{c}d_{f}}}}{T_{21} = {{T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\left\{ {{T_{21}\left\lbrack {{\left( {n_{c} + 1} \right)c_{1}},{n_{f}f_{0}}} \right\rbrack} - {T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\} d_{c}} + {\left\{ {{T_{21}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\} d_{f}} + {\left\{ {{T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{21}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{21}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{21}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack}} \right\} d_{c}d_{f}}}}{T_{22} = {{T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\left\{ {{T_{22}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\} d_{c}} + {\left\{ {{T_{22}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\} d_{f}} + {\left\{ {{T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{22}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{22}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{22}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack}} \right\} d_{c}d_{f}}}}} & \left\langle {{Equation}\mspace{14mu} 7} \right\rangle\end{matrix}$

Next, a method of measuring the data of S-parameters will be described.

[Measurement Circuit for Measuring S-Parameters]

FIG. 5 is a diagram showing a configuration of a measurement circuit formeasuring S-parameters of the impedance adjustment apparatus 3A. Themeasurement circuit shown in FIG. 5 is factory assembled, for example,before product shipment.

S-parameters of the impedance adjustment apparatus 3A are measured usinga network analyzer 80 having an input/output impedance of 50Ω, forexample. A first input/output terminal 81 of the network analyzer 80 isconnected to the input end 301 of the impedance adjustment apparatus 3A,and a second input/output terminal 82 of the network analyzer 80 isconnected to the output end 302 of the impedance adjustment apparatus3A. Also, a control terminal 83 of the network analyzer 80 is connectedto the control unit 100 of the impedance adjustment apparatus 3A.

[Procedure for Measuring S-Parameters]

The procedure for measuring S-parameters for individual sets ofcombination information (C,F) with respect to which the position of themovable portion of the variable capacitor 21 and the output frequency ofthe high frequency power source 1 v have been respectively changed atintervals of ten steps, as shown in Table 2, will be described, assumingthat the variation ranges of the position of the movable portion of thevariable capacitor 21 and the output frequency of the high frequencypower source 1 v are respectively 101 steps from 0 to 100.

In the measurement circuit shown in FIG. 5, S-parameters of theimpedance adjustment apparatus 3A are measured by the network analyzer80 while successively changing the combination information sets (C,F) ina predefined order. In the following description, the procedure forrespectively measuring S-parameters while successively changing theposition of the movable portion of the variable capacitor 21 and theoutput frequency at intervals of 10 will be described, assuming that thecombination information sets (C,F) at the grid points shown in Table 2are the measurement targets.

The position of the movable portion of the variable capacitor 21 and theoutput frequency of the network analyzer 80 are set to valuescorresponding to the initial set of combination information (C,F) by thecontrol unit 100. For example, when the initial set of combinationinformation (C,F) has been set to (0,0), the control unit 100 sets theposition of the movable portion of the variable capacitor 21 to aposition corresponding to “0”, for example, and sets the outputfrequency of the network analyzer 80 to a frequency (e.g., 1.8 MHz)corresponding to “0”, for example. This frequency is equivalent to theoutput frequency of the high frequency wave that is supplied from thehigh frequency power source 1 v to the load 5.

The network analyzer 80 first outputs a high frequency wave having afrequency (e.g., 1.8 MHz) corresponding to “0” from the firstinput/output terminal 81. The high frequency wave (incident wave) outputfrom the first input/output terminal 81 is partially reflected by theinput end 301 of the impedance adjustment apparatus 3A, and theremainder of the high frequency wave is input to the impedanceadjustment apparatus 3A. The high frequency wave (reflected wave)reflected by the input end 301 of the impedance adjustment apparatus 3Ais input from the first input/output terminal 81 into the networkanalyzer 80. The high frequency wave (transmitted wave) input into theimpedance adjustment apparatus 3A from the input end 301 is output fromthe output end 302, and is input into the network analyzer 80 from thesecond input/output terminal 82.

The network analyzer 80 detects the reflected wave input from the firstinput/output terminal 81 and the transmitted wave input from the secondinput/output terminal 82. The network analyzer 80 measures the voltagereflection coefficient (element S₁₁ of S-parameter) on the input sideand the transmission coefficient (element S₂₁ of S-parameter) of theforward voltage, using the detected values of the reflected wave andtransmitted wave and the incident wave. That is, when the incident wave,the reflected wave and the transmitted wave are given respectively asa1, b1 and b2, the network analyzer 80 measures the voltage reflectioncoefficient (S₁₁) and the transmission coefficient (S₂₁) of the forwardvoltage by calculating S₁₁=b1/a1 and S₂₁=b2/a1.

Next, the network analyzer 80 outputs a high frequency wave having afrequency (e.g., 1.8 MHz) corresponding to “0” from the secondinput/output terminal 82. The high frequency wave (incident wave) outputfrom the second input/output terminal 81 is partially reflected by theoutput end 302 of the impedance adjustment apparatus 3A, and theremainder of the high frequency wave is input to the impedanceadjustment apparatus 3A. The high frequency wave (reflected wave)reflected by the output end 302 of the impedance adjustment apparatus 3Ais input into the network analyzer 80 from the second input/outputterminal 82. The high frequency wave (transmitted wave) input into theimpedance adjustment apparatus 3A from the output end 302 is output fromthe input end 301 and input to the network analyzer 80 from the firstinput/output terminal 81.

The network analyzer 80 detects the reflected wave input from the secondinput/output terminal 82 and the transmitted wave input from the firstinput/output terminal 81. The network analyzer 80 then measures thetransmission coefficient (element S₁₂ of S-parameter) of the reversevoltage and the voltage reflection coefficient (element S₂₂ ofS-parameter) on the output side, using the detected values of thereflected wave and transmitted wave and the incident wave. That is, whenthe incident wave, the reflected wave and the transmitted wave are givenrespectively as a2, b2 and b1, the network analyzer 80 measures thetransmission coefficient (S₁₂) of the reverse voltage and the voltagereflection coefficient (S₂₂) on the output side, by calculatingS₁₂=b1/a2, and S₂₂=b2/a2.

As a result of the above two types of measurement processing, thetransmission coefficient (S₂₁) of the forward voltage, the transmissioncoefficient (S₁₂) of the reverse voltage, and the voltage reflectioncoefficient (S₂₂) on the output side that constitute the S-parameter“S(0,0)” with respect to the initial set of combination information(0,0) will be measured. The network analyzer 80 transmits the measuredvalues of S-parameter “S(0,0)” from the control terminal 83 to thecontrol unit 100 of the impedance adjustment apparatus 3A.

The control unit 100, on receiving the measured value of the S-parameter“S(0,0)”, converts the S-parameter “S(0,0)” into the T-parameter“T(0,0)” using the above Equation 2. The control unit 100 then storesthe resultant T-parameter “T(0,0)” in the memory 70 in association withthe combination information (0,0).

Thereafter, the control unit 100 measures the S-parameter “S(C,F)” foreach set of combination information (C,F) using the network analyzer 80,by successively changing the combination information (C,F) of theposition of the movable portion of the variable capacitor 21 and thefrequency of the high frequency output from the network analyzer 80. Thecontrol unit 100 measures the S-parameter “S(C,F)” corresponding to eachset of combination information (C,F) using the network analyzer 80,while successively changing the sets of combination information (C,F) inan order such as the following: S(0,0), S(0,10), . . . , S(0,90),S(0,100), S(10,0), S(10,10), . . . , S(100,90), S(100,100). It should beobvious that the order in which measurement is performed is not limitedto this order. The control unit 100 converts the measured value into aT-parameter “T(C,F)” every time an S-parameter “S(C,F)” for acombination information set (C,F) is measured by the network analyzer80, and stores the resultant T-parameter in the memory 70 in associationwith the combination information (C,F).

Note that, in the above measurement procedure, every time an S-parameteris measured, processing for converting the S-parameter into aT-parameter is performed, but the measurement procedure is not limitedthereto, and a configuration may be adopted in which conversion into aT-parameter is performed every plurality of S-parameters that aremeasured. Also, a configuration may be adopted in which the S-parametersfor all sets of combination information (C,F) serving as measurementtargets are first measured, before collectively converting the measuredvalues of the S-parameters into T-parameters. For this purpose, both amemory for S-parameters, and a memory for T-parameters can be providedif needed.

Also, a configuration may be adopted in which the data of theS-parameters or T-parameters is output to a display (not shown) of thenetwork analyzer 80 or a display, a printer (all not shown) or the likeprovided outside of the impedance adjustment apparatus 3A. It should beobvious that this data may be output to various external apparatuses(not shown).

[Operation of Impedance Adjustment Apparatus 3A]

Next, the impedance matching operation of the impedance adjustmentapparatus 3A that is actually used as a high frequency power supplysystem will be described with reference to FIG. 6.

FIG. 6 is a functional block diagram of the control unit 100. Thecontrol unit 100 is, from a functional viewpoint, constituted by avectorization unit 110, a frequency detection unit 120, a T-parameteracquisition unit 130, an output reflection coefficient calculation unit140, a target input reflection coefficient setting unit 150, a targetinformation specifying unit 180, a target position setting unit 191, anda target frequency setting unit 192, as shown in FIG. 6. The travelingwave voltage and reflected wave voltage that are output from thedirectional coupler 10 are input to the vectorization unit 110. Theposition information of the movable portion of the variable capacitor 21that is output from the position detection unit 40 is input to theT-parameter acquisition unit 130. The power source recognition outputfrequency F_(ge) that is output from the high frequency power source 1 vis input to the target frequency setting unit 192. The output frequencyinformation F_(mat) that is output from the control unit 100 to the highfrequency power source 1 v is generated by the target frequency settingunit 192, and the command signal (target position information C_(mat)discussed later) that is output from the control unit 100 to theadjustment unit 30 is generated by the target position setting unit 191.

Note that the frequency detection unit 120 is an example of an outputfrequency acquisition unit or frequency detection unit of the presentinvention, and the T-parameter acquisition unit 130 is an example of acharacteristic parameter acquisition unit of the present invention.Also, the output reflection coefficient calculation unit 140 is anexample of an output reflection coefficient calculation unit of thepresent invention, and the target information specifying unit 180 is anexample of a specifying unit of the present invention. Also, the targetfrequency setting unit 192 is an example of a command signal output unitof the present invention.

Note that the control unit 100 periodically repeats the impedancematching operation during the period from the start to the end of plasmaprocessing, and performs control such that the impedance of the highfrequency power source 1 v and the impedance of the load 5 are matched.Hereinafter, the processing from the start to the end of the impedancematching operation that is performed by the control unit 100 will bedescribed in detail. Also, in the following description, the point intime when each impedance matching operation is started will be calledthe “current point in time”.

The vectorization unit 110 is provided with an A/D converter (not shown)that samples an analog signal at a predetermined interval and convertsthe analog signal into a digital signal. The vectorization unit 110converts the traveling wave voltage and reflected wave voltage that areinput from the directional coupler 10 into respective digital signalsusing the A/D converter, and generates a traveling wave voltageVfi_(now) that is represented by vector information including size andphase information from the traveling wave voltage after conversion, anda reflected wave voltage Vri_(now) that is represented by vectorinformation including size and phase information from the reflected wavevoltage after conversion. The traveling wave voltage Vfi_(now) andreflected wave voltage Vri_(now) are the traveling wave voltage and thereflected wave voltage of the input end 301 at the current point intime.

In the case where a high frequency detector is used instead of thedirectional coupler 10, the vectorization unit 110 is provided with anA/D converter that converts the high frequency voltage and highfrequency current output from the high frequency detector intorespective digital signals. The vectorization unit 110 generates thetraveling wave voltage Vfi_(now) and the reflected wave voltageVri_(now) by a well-known method, using the high frequency voltage andthe high frequency current that were converted into digital signals.

In this case, a portion that includes the high frequency detector and apart that derives the traveling wave voltage Vfi_(now) and the reflectedwave voltage Vri_(now) based on detection signals of the high frequencydetector is an example of a high frequency information detection unit ofthe present invention.

The traveling wave voltage Vfi_(now) at the current point in timegenerated by the vectorization unit 110 is input to the outputreflection coefficient calculation unit 140 and the frequency detectionunit 120, and the reflected wave voltage Vri_(now) at the current pointin time generated by the vectorization unit 110 is input to the outputreflection coefficient calculation unit 140.

As shown in Equation 8, a reflection coefficient Γin_(now) (hereinafter,input reflection coefficient Γin_(now)) of the input end 301 at thecurrent point in time can be obtained, by dividing the reflected wavevoltage Vri_(now) by the traveling wave voltage Vfi_(now). Note that theabsolute value of the input reflection coefficient Γin_(now) (inputreflection coefficient absolute value) is |Γin_(now)|.

$\begin{matrix}{{\Gamma\;{in}\mspace{14mu}{now}} = \frac{V\; r\; i\mspace{14mu}{now}}{V\; f\; i\mspace{14mu}{now}}} & \left\langle {{Equation}\mspace{14mu} 8} \right\rangle\end{matrix}$

The frequency detection unit 120 detects the output frequency F_(now) atthe current point in time of the high frequency wave that is output fromthe high frequency power source 1 v by a well-known frequency detectionmethod, using the traveling wave voltage Vfi_(now) input from thevectorization unit 110. The output frequency F_(now) at the currentpoint in time detected by the frequency detection unit 120 is input tothe T-parameter acquisition unit 130 and the target frequency settingunit 192. Note that well-known frequency detection methods include, forexample, a frequency detection method that uses PLL (phase-locked loop)and a frequency detection method that uses zero crossing. It should beobvious that the frequency detection method is not limited to thesefrequency detection methods, and other frequency detection methods maybe used.

In the case where a high frequency detector is used instead of thedirectional coupler 10, the detected value of the high frequency voltagecan be input from the high frequency detector to the frequency detectionunit 120, for example, and the output frequency F_(now) at the currentpoint in time of the high frequency wave that is output from the highfrequency power source 1 v can be detected by the frequency detectionunit 120 using the detected values of the high frequency voltage.

As described above, the S-parameters used in the present embodiment areparameters that are measured while matching the frequency of the highfrequency wave that is output from the network analyzer 80 to the outputfrequency of the high frequency output from the high frequency powersource 1 v. For this reason, the difference between the output frequencyF_(now) at the current point in time detected by the frequency detectionunit 120 and the frequency of the high frequency output from the networkanalyzer 80 at the time that an S-parameter is measured needs to bereduced as much as possible.

From a similar viewpoint, the difference between the power sourcerecognition output frequency F_(ge) that is input from the highfrequency power source 1 v to the control unit 100 and the outputfrequency F_(now) at the current point in time that is detected by thefrequency detection unit 120 needs to be reduced as much as possible. Ifthe manufacturer of the high frequency power source 1 v is the same asthe manufacturer of the impedance adjustment apparatus 3A, thedifference between the power source recognition output frequency F_(ge)and the output frequency F_(now) can be reduced as much as possible.However, in the case where the manufacturer of the high frequency powersource 1 v differs from the manufacturer of the impedance adjustmentapparatus 3A, a difference could possibly occur between the power sourcerecognition output frequency F_(ge) and the output frequency F_(now),preventing accurate impedance matching from being performed. For thisreason, in the present embodiment, a configuration is adopted in whichthe output frequency of the high frequency wave that is output from thehigh frequency power source 1 v is detected by the control unit 100 ofthe impedance adjustment apparatus 3A.

It should be obvious that in the case where the power source recognitionoutput frequency F_(ge) and the output frequency F_(now) at the currentpoint in time are almost the same, a configuration can be adopted inwhich the frequency detection unit 120 is omitted, and the power sourcerecognition output frequency F_(ge) that is input from the highfrequency power source 1 v to the control unit 100 is input to theT-parameter acquisition unit 130 provided in the control unit 100.

The T-parameter acquisition unit 130 acquires a T-parametercorresponding to the combination of position information C_(now) at thecurrent point in time that is input from the position detection unit 40and an output frequency F_(now) at the current point in time that isinput from the frequency detection unit 120, using the T-parametersstored in the memory 70, and inputs the acquired T-parameter to theoutput reflection coefficient calculation unit 140.

The T-parameter acquisition unit 130, in the case where the T-parametercorresponding to the combination of the position information C_(now) andthe output frequency F_(now) at the current point in time is stored inthe memory 70, reads that T-parameter from the memory 70, and inputs theread T-parameter to the output reflection coefficient calculation unit140. In the case where the T-parameter corresponding to the combinationof position information C_(now) and the output frequency F_(now) at thecurrent point in time is not stored in the memory 70, the T-parameteracquisition unit 130 computes the T-parameter corresponding to thecombination of the position information C_(now) and the output frequencyF_(now) at the current point in time by the abovementioned interpolationoperation, using the T-parameters stored in the memory 70, and inputsthe computed value to the output reflection coefficient calculation unit140.

The output reflection coefficient calculation unit 140 calculates atraveling wave voltage Vfo_(now) and a reflected wave voltage Vro_(now)of the output end 302 at the current point in time, based on thetraveling wave voltage Vfi_(now) and the reflected wave voltageVri_(now) of the input end 301 at the current point in time that areinput from the vectorization unit 110 and the T-parameter correspondingto the combination of the position information C_(now) and the outputfrequency F_(now) at the current point in time that is input from theT-parameter acquisition unit 130. The output reflection coefficientcalculation unit 140 calculates the traveling wave voltage Vfo_(now) andthe reflected wave voltage Vro_(now) of the output end 302 at thecurrent point in time with Equation 9 shown below.

$\begin{matrix}{{\begin{bmatrix}{V\; f\; o\mspace{14mu}{now}} \\{V\; r\; o\mspace{14mu}{now}}\end{bmatrix} = {\begin{bmatrix}{T_{11}\mspace{11mu}{now}} & {T_{12\mspace{11mu}}\;{now}} \\{T_{21}\mspace{11mu}{now}} & {T_{22}\mspace{11mu}{now}}\end{bmatrix}\begin{bmatrix}{V\; f\; i\mspace{14mu}{now}} \\{V\; r\; i\mspace{14mu}{now}}\end{bmatrix}}}{{V\; f\; o\mspace{14mu}{now}} = {{T_{11}\mspace{11mu}{{now} \cdot V}\; f\; i\mspace{14mu}{now}} + {T_{12}\mspace{11mu}{{now} \cdot V}\; r\; i\mspace{14mu}{now}}}}{{V\; r\; o\mspace{14mu}{now}} = {{T_{21}\mspace{11mu}{{now} \cdot V}\; f\; i\mspace{14mu}{now}} + {T_{22}\mspace{11mu}{{now} \cdot V}\; r\; i\mspace{14mu}{now}}}}} & \left\langle {{Equation}\mspace{14mu} 9} \right\rangle\end{matrix}$

Note that, in Equation 9, T_(11now), T_(12now), T_(21now) and T_(22now)are elements constituting the T-parameter input from the T-parameteracquisition unit 130; that is, elements of the T-parameter correspondingto the combination of the position of the movable portion of thevariable capacitor 21 and the output frequency of the high frequencypower source 1 v at the current point in time.

Also, the output reflection coefficient calculation unit 140 calculatesa reflection coefficient Γout_(now) (hereinafter, output reflectioncoefficient Γout_(now)) of the output end 302 at the current point intime, by dividing the reflected wave voltage Vro_(now) of the output end302 at the current point in time by the traveling wave voltageVfo_(now), as shown in Equation 10. The calculation result is sent tothe target information specifying unit 180.

$\begin{matrix}{{\Gamma\;{out}\mspace{14mu}{now}} = \frac{V\; r\; o\mspace{14mu}{now}}{V\; f\; o\mspace{14mu}{now}}} & \left\langle {{Equation}\mspace{14mu} 10} \right\rangle\end{matrix}$

Note that output reflection coefficient Γout_(now) at the current pointin time can also be calculated by the following Equation 11 using theT-parameter.

$\begin{matrix}{{\Gamma\;{out}\mspace{14mu}{now}} = \frac{{T_{21}\mspace{11mu}{now}} + {T_{22}\mspace{11mu}{{now} \cdot \Gamma}\;{in}\mspace{14mu}{now}}}{{T_{11}\mspace{11mu}{now}} + {T_{12}\mspace{11mu}{{now} \cdot \Gamma}\;{in}\mspace{14mu}{now}}}} & \left\langle {{Equation}\mspace{14mu} 11} \right\rangle\end{matrix}$

The target input reflection coefficient setting unit 150 sets an inputreflection coefficient Γin_(set) (hereinafter, “target input reflectioncoefficient Γin_(set)”) that serves as a target in advance. This targetinput reflection coefficient Γin_(set) can be represented by Equation12. The target input reflection coefficient setting unit 150 inputs theset target input reflection coefficient Γin_(set) to the targetinformation specifying unit 180.

$\begin{matrix}{{\Gamma\;{in}\mspace{14mu}{set}} = \frac{{Z\;{in}} - {Z\; o}}{{Z\;{in}} + {Z\; o}}} & \left\langle {{Equation}\mspace{14mu} 12} \right\rangle\end{matrix}$

In Equation 12, Z_(in) is the target impedance, and is represented byZ_(in)=R_(in)+jX_(in) which is the sum of the real part R_(in) and theimaginary part Xin. Also, Z_(o) is the characteristic impedance. Notethat the target input reflection coefficient setting unit 150 may setthe target input reflection coefficient Γin_(set) directly, or aconfiguration may be adopted in which the target impedance Z_(in) andthe characteristic impedance Z_(o) are set in the target inputreflection coefficient setting unit 150 in advance, and the target inputreflection coefficient setting unit 150 sets the target input reflectioncoefficient Γin_(set) by calculating Equation 12 with the set targetimpedance Z_(in) and characteristic impedance Z_(o).

The target input reflection coefficient Γin_(set) is usually a minimumvalue, that is, 0 (Γin_(set)=0+j0 in the case where the target inputreflection coefficient Γin_(set) is represented by the sum of the realpart and the imaginary part), but may be set a value other than 0 thatcan be regarded as being matched. For example, the target inputreflection coefficient Γin_(set) may be set to the relatively smallvalue such as 0.05 or 0.1. In the case where the target input reflectioncoefficient Γin_(set) is set to 0, an impedance matching state where thereflected wave of the input end 301 is a minimum value (i.e., 0) can beachieved when the input reflection coefficient Γin becomes the targetinput reflection coefficient Γin_(set) by adjusting the position of themovable portion of the variable capacitor 21 and the output frequency ofthe high frequency power source 1 v at the time.

Although the target input reflection coefficient setting unit 150 mayalso set the desired target input reflection coefficient Γin_(set) inadvance, a configuration may be adopted in which a setting unit forsetting the target input reflection coefficient Γin_(set) in the targetinput reflection coefficient setting unit 150 is provided to enable thetarget input reflection coefficient Γin_(set) to be changed at any time.

The relationship between the target input reflection coefficientΓin_(set), output reflection coefficient Γout_(now) at the current pointin time and the T-parameter is represented as in Equation 13.

$\begin{matrix}{{\Gamma\;{out}\mspace{14mu}{now}} = \frac{{T_{21}{mat}} + {T_{22}{{mat} \cdot \Gamma}\;{in}\mspace{14mu}{set}}}{{T_{11}{mat}} + {T_{12}{{mat} \cdot \Gamma}\;{in}\mspace{14mu}{set}}}} & \left\langle {{Equation}\mspace{14mu} 13} \right\rangle\end{matrix}$

In Equation 13, T_(11mat), T_(12mat), T_(21mat) and T_(22mat) areelements of the T-parameter corresponding to the combination informationof the position of the movable portion of the variable capacitor 21 andthe output frequency of the high frequency power source 1 v that is ableto set the reflection coefficient of the input end 301 to the targetinput reflection coefficient Γin_(set), when the reflection coefficientof the output end 302 is the output reflection coefficient Γout_(now) atthe current point in time.

Equation 13 can be derived as follows. The output reflection coefficientΓout_(now) at the current point in time can be derived by Equation 10 orEquation 11. Also, the traveling wave voltage Vfo_(now) and thereflected wave voltage Vro_(now) of the output end 302 at the currentpoint in time are represented byVfo_(now)=T_(11mat)·Vfi_(now)+T_(12mat)·Vri_(now) andVro_(now)=T_(21mat)·Vfi_(now)+T_(22mat)·Vri_(now) (Vfi_(now) andVri_(now) are the traveling wave voltage and the reflected wave voltageof the input end 301 at the current point in time, if the T-parameter istaken into consideration with reference to Equation 9. Accordingly,Γout_(now)=(T_(21mat)·Vfinow+T_(22mat)·Vri_(now))/(T_(11mat)·Vfi_(now)+T_(12mat)·Vri_(now)).Here, because the input reflection coefficientΓin_(set)=Vri_(now)/Vfi_(now),Γout_(now)=[T_(21mat)·Vfi_(now)+T_(22mat)·(Γin_(set)·Vfi_(now))]/[T_(11mat)·Vfi_(now)+T_(12mat)·(Γin_(set)·Vfi_(now))]=(T_(21mat)+T_(22mat)·Γin_(set))/(T_(11mat)+T_(12mat)·Γin_(set)).

According to Equation 13, if the four elements (T_(11mat), T_(12mat),T_(21mat), T_(22mat)) of the T-parameter of the impedance adjustmentapparatus 3A can be adjusted such that Equation 13 is true, with respectto the output reflection coefficient Γout_(now) at the current point intime computed by the output reflection coefficient calculation unit 140,it is known that the input reflection coefficient Tin of the input end301 of the impedance adjustment circuit 3P can be set to the targetinput reflection coefficient Γin_(set) of the input end 301 of theimpedance adjustment circuit 3P.

If the four elements (T_(11mat), T_(12mat), T_(21mat), T_(22mat)) of aT-parameter can each be adjusted freely, a T-parameter (T_(11mat),T_(12mat), T_(21mat), T_(22mat)) for which Equation 13 is true can bederived.

However, because the T-parameter is a parameter representingtransmission characteristics at the time of treating the entireimpedance adjustment apparatus 3A as a transmission apparatus, and fourelements are measured as one set every combination of a position of themovable portion of the variable capacitor 21 and an output frequency ofthe high frequency power source 1 v, there is little possibility that avirtual output reflection coefficient Γout_(now)′ that matches theoutput reflection coefficient Γout_(now) at the current point in timewill be obtained.

The virtual output reflection coefficient Γout_(now)′ is represented byEquation 14, where the result of respectively substituting a pluralityof the T-parameters measured in advance such as shown in Table 3 or aplurality of parameters that are estimated by interpolation fromT-parameters measured in advance into the right side of Equation 13 istaken as the virtual output reflection coefficient Γout_(now)′.

$\begin{matrix}{{\Gamma\;{out}\mspace{14mu}{{now}^{\prime}\left( {C,F} \right)}} = \frac{{T_{21}{{mat}\left( {C,F} \right)}} + {T_{22}{{{mat}\left( {C,F} \right)} \cdot \Gamma}\;{in}\mspace{14mu}{set}}}{{T_{11}{{mat}\left( {C,F} \right)}} + {T_{12}{{{mat}\left( {C,F} \right)} \cdot \Gamma}\;{in}\mspace{14mu}{set}}}} & \left\langle {{Equation}\mspace{14mu} 14} \right\rangle\end{matrix}$

In Equation 14, T_(11mat)(C,F), T_(12mat)(C,F), T_(21mat)(C,F) andT_(22mat)(C,F) indicate elements of the T-parameter “T(C,F)”corresponding to the combination information (C,F), and Γout_(now)′(C,F)indicates the virtual output reflection coefficient corresponding tocombination information (C,F).

Although a plurality of virtual output reflection coefficientsΓout_(now)′(C,F) are obtained as a result of the calculation of Equation14, there is little possibility that a virtual output reflectioncoefficient Γout_(now)′(C,F) that matches the output reflectioncoefficient Γout_(now) at the current point in time will be obtained, asdescribed above.

However, a combination of the position of the movable portion of thevariable capacitor 21 and the output frequency of the high frequencypower source 1 v that most closely approximates the conditions underwhich Equation 13 is true can be specified, if the calculated virtualoutput reflection coefficients Γout_(now)′(C,F) are searched for avirtual output reflection coefficient Γout_(now)′(C,F) most closelyapproximately the output reflection coefficient Γout_(now) at thecurrent point in time (hereinafter, approximate reflection coefficientΓout_(now)″ (C,F)). Because the target input reflection coefficientΓin_(set) is set to be less than or equal to a value that can beregarded matched, as described above, the impedance can be regarded asmatched if an output reflection coefficient rout of the impedanceadjustment apparatus 3A can be set as the approximate reflectioncoefficient Γout_(now)″(C,F).

In the case where T-parameters are not acquired for all sets ofcombination information (C,F) of the position of the movable portion ofthe variable capacitor 21 and the output frequency of the high frequencypower source 1 v, as shown in Table 3, a combination information set(C,F) of the position of the movable portion of the variable capacitor21 and the output frequency of the high frequency power source 1 v thatmost closely approximates the conditions under which Equation 13 is truecannot be accuracy specified.

However, even if T-parameters (S-parameters) are not acquired for allsets of combination information (C,F), combination information of theposition of the movable portion of the variable capacitor 21 and theoutput frequency of the high frequency power source 1 v that mostclosely approximates (as close as possible) the conditions under whichEquation 13 is true can be specified through calculations. Thisspecification operation is performed in the target informationspecifying unit 180.

Note that, in the present specification, the combination informationthat most closely approximates the conditions under which Equation 13 istrue is referred to as “target combination information (Cz, Fz)”. Also,in the case where S-parameters are acquired for sets of combinationinformation (C,F) in a grid as shown in FIG. 2, for example, valuesobtained by converting those S-parameters are described as acquiredT-parameters. Note that, as described above, T-parameters converted fromS-parameters derived by interpolation can be included in the acquiredT-parameters. Hereinafter, the procedure of specifying targetcombination information (Cz, Fz) in the target information specifyingunit 180 will be described.

First, the method of specifying target combination information (Cz, Fz)will be described.

The relationship shown in Equation 15 is obtained by respectivelysubstituting T_(11mat), T_(12mat), T_(21mat), and T_(22mat) of Equation13 for the four elements T₁₁, T₁₂, T₂₁ and T₂₂ shown in Equation 7.

$\begin{matrix}{\mspace{85mu}{{{\Gamma\;{out}_{now}} = \frac{T_{21\;{mat}} + {T_{22\;{mat}}\Gamma\;{in}_{set}}}{T_{11\;{mat}} + {T_{12\;{mat}}\Gamma\;{in}_{set}}}}\mspace{79mu}{{T_{21\;{mat}} + {\Gamma\;{in}_{set}T_{22\;{mat}}} - {\Gamma\;{{out}_{now}\left( {T_{11\;{mat}} + {\Gamma\;{in}_{set}T_{12\;{mat}}}} \right)}}} = 0}{{T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}{T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} - {\Gamma\;{{out}_{now}\left\lbrack {{T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}{T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}}} \right\rbrack}} + {\quad{{\left\langle \begin{matrix}{{T_{21}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}\left\{ {{T_{22}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\}} -} \\{\Gamma\;{out}_{now}\left\langle {{T_{11}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}\left\{ {{T_{12}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\}}} \right\rangle}\end{matrix} \right\rangle d_{c}} + {\quad{{\left\langle \begin{matrix}{{T_{21}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}\left\{ {{T_{22}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\}} -} \\{\Gamma\;{out}_{now}\left\langle {{T_{11}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}\left\{ {{T_{12}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\}}} \right\rangle}\end{matrix} \right\rangle d_{f}} + {\quad{{\begin{bmatrix}{{T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{21}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{21}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{21}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} +} \\{{\Gamma\;{in}_{set}\left\{ {{T_{22}\left\lbrack {{n_{c}c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{22}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{22}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{22}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack}} \right\}} -} \\{\Gamma\;{out}_{now}\left\langle \begin{matrix}{{T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{11}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{11}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{11}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} +} \\{\Gamma\;{in}_{set}\left\{ {{T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{12}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{12}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{12}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack}} \right\}}\end{matrix} \right\rangle}\end{bmatrix}d_{c}d_{f}} = 0}}}}}}}}} & \left\langle {{Equation}\mspace{14mu} 15} \right\rangle\end{matrix}$

Substituting Equation 16 into Equation 15 gives Equation 17. With theseequations, it is only the first time and when the target inputreflection coefficient Γin_(set) is changed that it is possible toperform calculations for all combinations of n_(c) and n_(f) and tostore the results in a memory (not shown).

Note that, in Equation 17, A₁, A₂, B₁, B₂, C₁, C₂, D₁ and D₂ have beenpartially omitted, in order to simplify notation. For example, A1denotes A1(n_(c), n_(f), Γinset).

$\begin{matrix}{{{A_{1}\left( {n_{c},n_{f},{\Gamma\;{in}_{set}}} \right)} = {{T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}{T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}}}}{A_{2}\left( {n_{c},n_{f},{\Gamma\;{in}_{set}}} \right)} = {{T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}{T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}}}} & \left\langle {{Equation}\mspace{14mu} 16} \right\rangle \\{{{B_{1}\left( {n_{c},n_{f},{\Gamma\;{in}_{set}}} \right)} = {{T_{21}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}\left\{ {{T_{22}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\}}}}{{B_{2}\left( {n_{c},n_{f},{\Gamma\;{in}_{set}}} \right)} = {{T_{11}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}\left\{ {{T_{12}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\}}}}} & \; \\{{{C_{1}\left( {n_{c},n_{f},{\Gamma\;{in}_{set}}} \right)} = {{T_{21}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}\left\{ {{T_{22}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\}}}}{{C_{2}\left( {n_{c},n_{f},{\Gamma\;{in}_{set}}} \right)} = {{T_{11}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} + {\Gamma\;{in}_{set}\left\{ {{T_{12}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} - {T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)}} \right\}}}}} & \; \\{{D_{1}\left( {n_{c},n_{f},{\Gamma\;{in}_{set}}} \right)} = {{T_{21}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{21}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{21}\left\lbrack {{n_{c}c_{1}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{21}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {\Gamma\;{in}_{set}\left\{ {{{T_{22}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{22}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{22}\left. \quad{\left\lbrack {{n_{f}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack + {T_{22}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack}} \right\}{D_{2}\left( {n_{c},n_{f},{\Gamma\;{in}_{set}}} \right)}}} = {{T_{11}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{11}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{11}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{11}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {\Gamma\;{in}_{set}\left\{ {{T_{12}\left( {{n_{c}c_{0}},{n_{f}f_{0}}} \right)} - {T_{12}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{n_{f}f_{0}}} \right\rbrack} - {T_{12}\left\lbrack {{n_{c}c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack} + {T_{12}\left\lbrack {{\left( {n_{c} + 1} \right)c_{0}},{\left( {n_{f} + 1} \right)f_{0}}} \right\rbrack}} \right\}}}} \right.}}} & \; \\{{A_{1} - {\Gamma\;{out}_{now}A_{2}} + {\left( {B_{1} - {\Gamma\;{out}_{now}B_{2}}} \right){dc}} + {\left( {C_{1} - {\Gamma\;{out}_{now}C_{2}}} \right){df}} + {\left( {D_{1} - {\Gamma\;{out}_{now}D_{2}}} \right){dc}\mspace{11mu}{df}}} = 0} & \left\langle {{Equation}\mspace{14mu} 17} \right\rangle\end{matrix}$

Further substituting Equation 18 into Equation 17 gives Equation 19.Note that, in Equation 19, A, B, C and D have been partially omitted, inorder to simplify notation. For example, A denotes A(n_(c), n_(f),Γin_(set), Γout_(now)).A(nc,nf,Γin _(set),Γout_(now))=A1−Γout_(now) A2B(nc,nf,Γin _(set),Γout_(now))=B1−Γout_(now) B2C(nc,nf,Γin _(set),Γout_(now))=C1−Γout_(now) C2D(nc,nf,Γin _(set),Γout_(now))=D1−Γout_(now) D2  <Equation 18>A+Bdc+Cdf+Ddcdf=0  <Equation 19>

The equation shown in Equation 20 can be obtained when Equation 19 isdivided into the real part and the imaginary part to derive d_(c) andd_(f).

$\begin{matrix}{{{{\left\{ {{{{Re}(B)}{{Im}(D)}} - {{{Re}(D)}{{Im}(B)}}} \right\} d_{c}^{2}} + {\left\{ {{{{Re}(A)}{{Im}(D)}} - {{{Re}(D)}{{Im}(A)}} + {{{Re}(B)}{{Im}(C)}} - {{{Re}(C)}{{Im}(B)}}} \right\} d_{c}} + {{{Re}(A)}{{Im}(C)}} - {{{Re}(C)}{{Im}(A)}}} = 0}\mspace{79mu}{d_{c} = \frac{{- \left\lbrack {{{{Re}(A)}{{Im}(D)}} - {{{Re}(D)}{{Im}(A)}} + {{{Re}(B)}{{Im}(C)}} - {{{Re}(C)}{{Im}(B)}}} \right\rbrack} \pm \sqrt{\begin{matrix}{\;{\left\lbrack {{{{Re}(A)}{{Im}(D)}} - {{{Re}(D)}{{Im}(A)}} + {{{Re}(B)}{{Im}(C)}} - {{{Re}(C)}{{Im}(B)}}} \right\rbrack^{2} -}} \\{4\left\{ {\left\lbrack {{{{Re}(B)}{{Im}(D)}} - {{{Re}(D)}{{Im}(B)}}} \right\rbrack\left\lbrack {{{{Re}(A)}{{Im}(C)}} - {{{Re}(C)}{{Im}(A)}}} \right\rbrack} \right\}}\end{matrix}}}{2\left\lbrack {{{{Re}(B)}{{Im}(D)}} - {{{Re}(D)}{{Im}(B)}}} \right\rbrack}}\mspace{79mu}{d_{f} = {- \frac{{{Re}(A)} + {{{Re}(B)}d_{c}}}{{{Re}(C)} + {{{Re}(D)}d_{c}}}}}} & \left\langle {{Equation}\mspace{14mu} 20} \right\rangle\end{matrix}$

Note that, in Equation 19, if A=Re(A)+Im(A), B=Re(B)+Im(B),C=Re(C)+Im(C) and D=Re(D)+Im(D), the real part and the imaginary part ofthe left side of Equation 19 are 0, thus giving:Re(A)+Re(B)d _(c) +Re(C)df+Re(D)d _(c) d _(f)=0Im(A)+Im(B)d _(c) +Im(C)df+Im(D)d _(c) d _(f)=0

Deriving d_(f) from these equations gives:d _(f)=−(Re(A)+Re(B)d _(c))/(Re(C)+Re(D)d _(c))d _(f)=−(Im(A)+Im(B)d _(c))/(Im(C)+Im(D)d _(c))

Thus, the following is obtained from these two equations:(Re(A)+Re(B)d _(c))−(Im(C)+Im(D)d _(c))=(Re(C)+Re(D)d_(c))−(Im(A)+Im(B)d _(c))

Transforming this equation gives the quadratic equation of d_(c) shownin Equation 20, and the equation of d_(c) shown in Equation 20 isobtained from the solution equation of this quadratic equation.

Because of the relationships shown in Equations 15 to 20, the targetcombination information (Cz, Fz) can be derived by deriving d_(c)(decimal part of C/c₀) and d_(f) (decimal part of C/c₀) from theequation of d_(c) and d_(f) shown in Equation 20, in all combinations ofn_(c) (integer part of C/c₀) and n_(f) (integer part of F/f₀), andextracting the combinations in which d_(c) and d_(f) are respectivelybetween 0 and 1. The target combination information (Cz, Fz) isrepresented by [(n_(c)+d_(c))c₀, f(n_(f)+d_(f))f₀](0<d_(c)<1,0<d_(f)<1).

Next, the procedure for deriving target combination information (Cz, Fz)will be described.

Referring to Equations 15 and 16, it is known that d_(c) and d_(f) in anarbitrary combination (n_(c), n_(f)) are derived using the T-parametersof four types of combinations n_(c)c₀, c(n_(c)+1)₀, n_(f)f₀ andf(n_(f)+1)₀.

For example, because (n_(c)+1, n_(f))=(1,0), =(n_(c), n_(f)+1)=(0,1) and(n_(c)+1, n_(f)+1)=(1,1) when (n_(c), n_(f))=(0,0), d_(c) and d_(f) arederived using the four T-parameters of the combinations (0,0), (c₀, 0),(0, f₀) and (c₀, f₀). At this time, if the data intervals n₀ and n_(f)of known T-parameters are respectively 10 as shown in FIG. 2, d_(c) andd_(f) are derived using the four T-parameters T(0,0), T(10,0), T(0,10)and T(10,10).

Also, when (n_(c), n_(f))=(1,0), d_(c) and d_(f) are similarly derivedusing the four T-parameters T(10,0), T(20,0), T(10,10) and T(20,10).

Accordingly, d_(c) and d_(f) for all combinations (n_(c), n_(f)) ofn_(c) and n_(f) are derived by successively changing the values of thecombinations of n_(c) and n_(f), and repeating processing for derivingd_(c) and d_(f) using the four T-parameters corresponding to eachcombination (n_(c), n_(f)).

Note that in the case where T-parameters are acquired for combinationsat grid points, as shown in FIG. 2, the ranges of n_(c) and n_(f) thatis used in calculating d_(c) and d_(f) are respectively n_(c)=0-10, andn_(f)=0-10, but because n_(c)=10 is included in the four combinationsincluding n_(c)=9 and n_(f)=10 is included in the four combinationsincluding n_(f)=9, n_(c) and n_(f) can be respectively changed to valueswithin the range 0-9 in the processing for successively changing thevalues of the combinations of n_(c) and n_(f).

Accordingly, if the maximum value of the variation range of n_(c) isgiven as “n_(cmax)” and the maximum value of the variation range ofn_(f) is given as “n_(fmax)”, d_(c) and d_(f) for all of thecombinations of n_(c) and n_(f) can be derived by changing n_(c) in arange of 0 to (n_(cmax)−1) and changing n_(f) in a range of 0 to(n_(fmax)−1).

FIG. 7 is a diagram showing an exemplary way of changing the variablesn_(c) and n_(f) that are used for specifying target combinationinformation (Cz, Fz).

In FIG. 7, n_(c) is set on the horizontal axis, n_(f) is set on thevertical axis, and an area enclosed by four points of the combinations(n_(c), n_(f)) of n_(c) and n_(f) is represented by X(n_(c), n_(f)). Forexample, when (n_(c), n_(f))=(0,0), the area X(0,0) is an area enclosedby the four points (n_(c), n_(f))=(0,0), (10,0), (0,10) and (10,10).

Accordingly, when the values of n_(c) and n_(f) are successively changedsuch that (n_(c), n_(f))=(0,0)→(1,0)→(2, 0) . . . (8, 0)→(9,0)→(0,1)→(1,1) (2, 1) . . . (8, 1)→(9, 1)→(0,2)→(1,2)→(2, 2) . . . (8,9)→(9, 9), for example, as shown by the arrows in FIG. 7, the areatargeted for performing calculations changes such thatX(0,0)→X(1,0)→X(2, 0) . . . X(8, 0)→X(9, 0)→X(0,1)→X(1,1)→X(2, 1) . . .X(8, 1)→X(9, 1) X(0,2)→X(1,2)→X(2, 2) . . . X(8, 9)→X(9, 9), thusenabling d_(c) and d_(f) to be derived for all combinations of the n;and n_(f).

That is, as described above, if the values of n_(c) and n_(f) arechanged in the ranges n_(c)=0 to (nc_(max)−1) and n_(f) =0 to(nf_(max)−1), d_(c) and d_(f) can be derived for all combinations of then_(c) and n_(f).

It should be obvious that the way of changing of the values of thevariables n_(c) and n_(f) is not limited to that described above, andthe values of these variables may be changed in other ways.

In the case where d_(c) and d_(f) are derived using the equations ofd_(c) and d_(f) shown in Equation 20, d_(c) and d_(f) will not takevalues between 0 and 1 in some cases. For example, in the case where(n_(c), n_(f))=(0,0), that is, in the case where an area “X(0,0)” istargeted, d_(c) and d_(f) will not take values between 0 and 1 in somecases. In such cases, the target combination information (Cz, Fz) willexist outside the area “X(0,0)”. In FIG. 7, the area “X(0,0)” is an areaenclosed by the four points (n_(c), n_(f))=(0,0), (10,0), (0,10) and(10,10), but in the case where d_(c) and d_(f) do not take valuesbetween 0 and 1, the target combination information (Cz, Fz) will existin another area rather than that area. In the case where d_(c) and d_(f)do not take values between 0 and 1 in the other area, the targetcombination information (Cz, Fz) will exist outside that area.

Errors also occur in d_(c) and d_(f) due to factors such as detectionerror in detecting the input reflection coefficient absolute value|Γin_(now)|. This error tends to increase as input reflectioncoefficient absolute value |Γin_(now)| increases. Because the accuracyof the specified target combination information (Cz, Fz) will be low dueto errors in d_(c) and d_(f) in a state where the input reflectioncoefficient absolute value |Γin_(now)| takes a large value, aconfiguration may be adopted in which the adjustment circuit 3A isadjusted to that target combination information (F) to reduce the inputreflection coefficient absolute value |Γin_(now)|, before again derivingd_(c) and d_(f) and specifying the target combination information (Cz,Fz).

Also, it is conceivable that a plurality of combinations of n_(c) andn_(f) in which d_(c) and d_(f) take values between 0 and 1 may occur. Insuch cases, a configuration may be adopted in which, for example, thetarget combination information (Cz, Fz) is specified based on any onecombination of n_(c) and n_(f) and the adjustment circuit 3A is adjustedto the target combination information (Cz, Fz), before again derivingd_(c) and d_(f) and specifying the target combination information (Cz,Fz).

Also, in the case where d_(c) and d_(f) do not take values between 0 and1 in any of the combinations of n_(c) and n_(f), a configuration may beadopted in which, for example, the input reflection coefficient Γin iscalculated in all combinations of n_(c) and n_(f) when d_(c) and d_(f)are set to 0, and the target combination information (Cz, Fz) isspecified, based on n_(c) and n_(f) corresponding to the inputreflection coefficient Γin that most closely approximates the targetinput reflection coefficient Γin_(set).

In the above description, processing for specifying the targetcombination information (Cz, Fz) is performed after deriving d_(c) andd_(f) for all combinations of n_(c) and n_(f), but the processing forspecifying the target combination information (Cz, Fz) may be performedfor a portion of the combinations of n_(c) and n_(f). For example, itmay be judged whether d_(c) and d_(f) take values between 0 and 1 everytime d_(c) and d_(f) are computed, and if d_(c) and d_(f) do take valuesbetween 0 and 1, the target combination information (Cz, Fz) may bespecified, based on the calculated result of d_(c) and d_(f) at thattime.

The position information C of the movable portion of the variablecapacitor 21 and the output frequency information F of the highfrequency power source 1 v are included in (associated with) thespecified target combination information (Cz, Fz). The reflectioncoefficient Γin of the input end 301 of the impedance adjustmentapparatus 3A can be approximated to the target input reflectioncoefficient Γinset, when the position of the movable portion of thevariable capacitor 21 is adjusted to a position corresponding to theposition information C associated with target combination information(Cz, Fz), and the output frequency of the high frequency power source 1v is adjusted to a frequency corresponding to the output frequencyinformation F associated with the target combination information (Cz,Fz). That is, the high frequency power source 1 v and the load 5 can beapproximated to an impedance matching state. Usually, a state where theimpedances of the high frequency power source 1 v and the load 5 areregarded as being matched can be achieved. For this reason, processingfor respectively adjusting the position of the movable portion of thevariable capacitor 21 and the output frequency of the high frequencypower source 1 v to a position corresponding to the position informationC and a frequency corresponding to the output frequency information Fassociated with the target combination information (Cz, Fz) isperformed, as shown below.

The target position setting unit 191 sets the position corresponding tothe position information Cz of the target combination information (Cz,Fz) specified by the target information specifying unit 180 as thetarget position C_(mat). The target position C_(mat) is an example oftarget electrical characteristic information of the present invention.The target position setting unit 191 generates the target positioninformation C_(mat) for adjusting (displacing) the position of themovable portion of the variable capacitor 21 to the target positionC_(mat), and outputs the generated target position information C_(mat)to the adjustment unit 30. The target position setting unit 191 outputsthe target position information C_(mat) to the adjustment unit 30 as asignal of a form suitable for driving the adjustment unit 30, such as avoltage signal or a pulse signal, for example.

The adjustment unit 30 drives the stepping motor and the like based onthe target position information C_(mat), and adjusts (displaces) theposition of the movable portion of the variable capacitor 21 to thetarget position C_(mat).

The target frequency setting unit 192 sets the frequency correspondingto the output frequency information Fz of the target combinationinformation (Cz, Fz) specified by the target information specifying unit180 as the target output frequency Fac. The target the output frequencyF_(mat) is an example of target output frequency information of thepresent invention. The target frequency setting unit 192 generates thetarget output frequency information F_(mat) for adjusting (changing) theoutput frequency of the high frequency power source 1 v to the targetoutput frequency F_(mat), and outputs the generated target outputfrequency information F_(mat) to the high frequency power source 1 v.The target frequency setting unit 192 outputs the target outputfrequency information F_(mat) to the adjustment unit 30 in a formsuitable for transmission to the high frequency power source 1 v.

The high frequency power source 1 v adjusts (changes) the outputfrequency to the target output frequency F_(mat), based on the targetoutput frequency information F_(mat).

Here, supplementary description of the target output frequencyinformation F_(mat) will be given.

As described above, a difference (error) may occur between the powersource recognition output frequency F_(ge) that is recognized by thehigh frequency power source 1 v and the output frequency F_(now) at thecurrent point in time that is detected by the frequency detection unit120 (output frequency F_(now) at the current point in time that isrecognized by the impedance adjustment apparatus 3), due to themanufacturer of the high frequency power source 1 v differing from themanufacturer of the impedance adjustment apparatus 3.

In this case, because accurate impedance matching cannot be performed, afrequency obtained by adding the power source recognition outputfrequency F_(ge) to the difference between the target output frequencyF_(mat) and the output frequency F_(now) at the current point in time isset as the target frequency information F_(mat), as shown in Equation21. Because this results in target output frequency information F_(mat)that takes consideration of the difference (error) between the powersource recognition output frequency F_(ge) and the output frequencyF_(now) at the current point in time that is recognized by the impedanceadjustment apparatus 3 being output to the high frequency power source 1v, accurate impedance matching can be performed, even in the case wherea difference (error) arises between the power source recognition outputfrequency F_(ge) and the output frequency F_(now) at the current pointin time.F _(mat)=(f _(mat) −F _(now))+F _(ge)  <Equation 21>

Alternatively, a configuration may be adopted in which the differencebetween the target output frequency F_(mat) and the output frequencyF_(now) at the current point in time is output to the high frequencypower source 1 v as the target frequency information F_(mat), as inEquation 22, and a frequency obtained by adding the power sourcerecognition output frequency F_(ge) to the target frequency informationF_(mat) at the high frequency power source 1 v side is output. Thisenables accurate impedance matching to be performed, even in the casewhere a difference occurs between the power source recognition outputfrequency F_(ge) and the output frequency F_(now) at the current pointin time.F _(mat) =f _(mat) −F _(now)  <Equation 22>

Note that this invention is not limited to the embodiments describedabove. For example, the characteristic parameters are not limited toS-parameters or T-parameters. A configuration may be adopted in which Zparameters or Y parameters are used as characteristic parameters, andthe abovementioned impedance matching is performed by converting theseparameters into the abovementioned T-parameters.

The invention claimed is:
 1. A high frequency matching system comprising: a high frequency power supply for supplying high frequency power to a load; an impedance adjuster for adjusting a target impedance seen from the high frequency power supply to the load; a variable electrical characteristic element; a characteristic parameter storage unit for storing a plurality of characteristic parameters indicating transmission characteristics of the impedance adjuster, the plurality of characteristic parameters being parameters that are respectively acquired for a plurality of adjustment points at which a plurality of frequency adjustment points that correspond to output frequencies of the high frequency power supply are combined with a plurality of electrical characteristic adjustment points that correspond to electrical characteristics of the variable electrical characteristic element; a high frequency information detection unit for detecting high frequency information of an output end of the high frequency power supply or of an input end of the impedance adjuster; an electrical characteristic acquisition unit for acquiring an electrical characteristic of the variable electrical characteristic element; a characteristic parameter acquisition unit for acquiring a characteristic parameter for an adjustment point at which an output frequency of the high frequency power supply is combined with the acquired electrical characteristic, based on the plurality of characteristic parameters; an output reflection coefficient calculation unit for calculating an output reflection coefficient of an output end of the impedance adjuster, based on the high frequency information detected by the high frequency information detection unit and the characteristic parameter acquired by the characteristic parameter acquisition unit; a specifying unit for specifying an impedance adjustment point at which to match the target impedance to the impedance of the high frequency power supply, among the plurality of adjustment points, based on the output reflection coefficient, a target input reflection coefficient set in advance, and the plurality of characteristic parameters; an electrical characteristic element adjustment unit for adjusting the electrical characteristic of the variable electrical characteristic element to an electrical characteristic of the impedance adjustment point; and a command signal output unit for outputting, to the high frequency power supply, a command signal for adjusting the output frequency of the high frequency power supply to an output frequency of the impedance adjustment point.
 2. The high frequency matching system according to claim 1, wherein the characteristic parameter storage unit stores characteristic parameters measured for every adjustment point, or characteristic parameters that are converted from the measured characteristic parameters and are different in type from the measured characteristic parameters.
 3. The high frequency matching system according to claim 2, wherein the measured characteristic parameters are S-parameters (scattering parameters) and the characteristic parameters that are different in type from the measured characteristic parameters are T-parameters (transmission parameters).
 4. The high frequency matching system according to claim 1, wherein the plurality of characteristic parameters that are stored in the characteristic parameter storage unit include actual values measured at each adjustment point with respect to a portion of the plurality of adjustment points, and estimated values computed at each adjustment point by interpolation using the actual values with respect to adjustment points that have not been measured among the plurality of adjustment points.
 5. The high frequency matching system according to claim 4, wherein the adjustment points at which the characteristic parameters were measured are adjustment points at which a portion of frequency adjustment points extracted at a first interval from the plurality of frequency adjustment points are combined with a portion of electrical characteristic adjustment points extracted at a second interval from the plurality of electrical characteristic adjustment points.
 6. The high frequency matching system according to claim 1, wherein the specifying unit, based on the target input reflection coefficient and the plurality of characteristic parameters, calculates a virtual output reflection coefficient of the output end at each adjustment point assuming that the output frequency of the high frequency power supply and the electrical characteristic of the variable electrical characteristic element have been adjusted to the plurality of adjustment points, and specifies an adjustment point at which a difference between the output reflection coefficient and the virtual output reflection coefficient is smallest as an adjustment point of the target impedance.
 7. The high frequency matching system according to claim 1, wherein the high frequency information is a traveling wave voltage that travels from the high frequency power supply to the load and a reflected wave voltage that is reflected from the load to the high frequency power supply.
 8. The high frequency matching system according to claim 1, wherein the output reflection coefficient calculation unit calculates an input reflection coefficient of the input end based on the high frequency information, and calculates the output reflection coefficient based on the calculated input reflection coefficient and the acquired characteristic parameter. 